EDIT: I would recommend using the original Oblivion meshes rather than using the Skyblivion ones as when you export the collision model from the Oblivion meshes it is easier to edit rather than the Skyblivion meshes needing to go through "Chunk Extract" and for me it just separated it making it harder.
EDIT2: Please excuse my desktop as I play Skyrim in windowed mode and also I do realize theres more ways to do this but I find this the easiest. Have a nice day! :)
If you need oblivion models ask me and I will send you them.
You may have noticed when you walk around Cyrodiil or the Shivering Isles you encounter some steps which stops you from moving or you have to move or jump to free yourself. In the tutorial I shall tell you how to fix these steps. (Well try i'm bad at tutorials.)
Okay, to start of load up Skyblivion. Walk around and look for some buggy collisions on the stairs. I've found mine in the Imperial City Market District.
You may notice when your either walking or running you will get stuck on the steps. Take a picture or remember where you are in the world and load up either the Creation Kit for Skyrim or Oblivion (It really doesn't matter I just load up Oblivion's CSKit because it loads faster and theres less stuff to do.)
After you have found the location now you need to find out the name of the mesh you are going to fix. Mine is called "ICMarketStreet1". Your mesh name will obviously be different than this. If you do not know where the mesh is located you can probably see it by double clicking on it and finding the path where it is located. Mine is "Architecture/ImperialCity/NameOfMesh". Find the mesh in the Oblivion's ".Bsa". (You will need Oblivion's meshes and NOT Skyblivion meshes.)
If not, then you will need to use the Skyblivion's mesh instead. Be warned though. This might be different to the Oblivion's mesh. The reason I rely on Oblivion's mesh because it's easier to modify later in 3DS Max.
Okay. Step 3. Open your mesh into NIFSkope. This is the part where you really need to read, and to not skip! If you are not familiar with NIFSkope your interface is the following, on the left is all of the blocks(Or more complex term a Hierarchy). The right is the preview. The bottom for me is the properties.
If you are using the Oblivion mesh in the preview you should see red lines/boxes representing the collisions. If not, You will mostly likely be using a Skyblivion mesh. The export the collision, go to the top left of your window and press "File" then look for "Export" and Export it as an ".OBJ.". You can save it wherever you want to as it doesn't really matter. For this tutorial I will be using 3ds Max 12 and I know i'm 4 years behind but it works best with the current NIF Plugin. Go ahead and launch your 3ds max up if you have not already and when it has loaded, Import the ".OBJ" While you are importing you should encounter a screen with options how to import it. There should be a box with Multiple mesh names and one called "collision". Uncheck all the rest of them and just import the collision file and also remember to also uncheck the flip ZY option. You may be warned that there is not textures loaded just skip them as you don't need them in this tutorial.
When the model has been loaded into 3ds Max, it should be just a grey mesh which looks similar to the mesh in game.
When you have imported it the mesh should look like the one in game and the one in CSKIT. Congratulations if you are up to this stage you actually could understand my English! Anyway, back to fixing the collision mesh. If you look closely to the mesh you will see that the steps are not the best for the Skyrim NPC and Players and this is the thing we need to fix. To fix, press modify on the right and click "Editable Mesh" You can use any of the 5 choices to select the vertices. I would recommend the Element one and the Vertex one. Mainly if you need to click the whole of the step you can use Element and for the more annoying ones Vertex to get it 100% accurate. Watch this video to understand how to detach/split the stairs from the actual mesh. When you have highlighted all of the face/vertices click detach and name it as Stair. If theres multiple stairs in the model you will need to go back to the normal model and edit and detach again. To merge these detached meshes together all you have to do is click on one and then press the "Attach" button. Once done, press the other stair piece you want to merge. Meshes like the ICMarketStreet have multiple stair pieces you need to split from the main mesh so you this technique to help you.
You should see that the stairs are now split from the actual the model. Now it is done, you can export it. To export go to Export>NIF. Another interface will pop up. To be honest, i'm not to sure which options you select yet, but just copy the same options in the picture below.
Now the 3ds Max part is over, you can close it. Now go to where you saved the collision and open it up in Nifskope and you will see that the mesh is white and on the block list interface there is only four things. NiNode, BSXFlags and two NiTriShape's.
(Picture below is an old one and isn't the same but it still follows the tutorial.)
First of all, we need to change the NiNode to a BSFadeNode and you can delete the BSXFlags as that is not needed. (To delete click it and then press CTRL + DELETE). You should now be left with BSFadeNode and two NiTriShape's. If yes, Good! If no will then you have done something incorrectly. The next part isn't difficult. Next we have make the game realize it's either a material that lets the user walk up or if it's just a normal wall. So since my mesh is made out of stone, I will be going for "SKY_HAV_MAT_STAIRS_STONE" and "SKY_HAV_MAT_STONE". To add this into the NIF file we need to click the NiTriShape and change the Name to the ones above. If you get stuck you can always look at the video below. The part of the mesh which aren't stairs should be the one just named "SKY_HAV_MAT_STONE" and the part including stairs should be called "SKY_HAV_MAT_STAIRS_STONE".
Bam! There you go! This now should be the new collision file for the stairs you have converted. But it is not over yet! Now you have to implement it into the actual NIF for the stairs itself. Now I said earlier that we use the Oblivion files to get the collision file now we use the Skyblivion files to update the collision. To update the collision you will need to use the program called "NifUtilsSuite" It is very powerful and helps us for what we need. Once you have downloaded this program load it up. If it is your first time you will need to do the first time setup. I will help you set it up for the first time since I am such a kind person. :)
It should look like the above once you load up the program. To set it up first you will need to locate your "Nif.xml" file usually located in the same directory as Nifskope. Next is locating your Skyrim directory. If you have a cracked version then you are a very naughty person and should buy the real game! The normal Skyrim directory is usually in your steam library folder. Locate your TESV directory and then click "Data" and then click "Open". As I said earlier if you have a cracked version it will be elsewhere and you will need to go searching. Finally is Templates. I will be linking to my template in at the bottom of the page. Place it in a folder where you now it will be safe. For example I saved mine in my "Nifskope" directory so I know where it is. Once you have done that you have set "NifUtilSuite" and can now carry on with the tutorial. It should look like mine below this paragraph.
Once you have done that click next lots of times to finish the setup. Now you should be able to look around the program but we will be using "ChunkMerge" so click on the tab. You will need to change some options on this tab before you do anything else. Look at the picture below and compare to your own.
Okay now to the actual collision itself. The "Target-File" will need to be the Skyblivion mesh you want to change the collision of. So go ahead and locate it. The Collision file will need to be the one you just created and exported through 3ds max. When everything is done and correct go ahead and click "Add Collision" at the bottom right. There you go. Check the console to see "Collision data added successfully" This isn't the end sadly as now we need to test it ingame. not a hard thing to do. You must try out the new mesh in game.
You can see that I have fixed the collision file so now you walk up the steps with no bugging out and doesn't annoy people anymore. The second time Is just to show the difference. You should now be very pleased of yourself!
If you need any help just PM me and I will get back to you. I'm not usually on but I will try to be on more than usual just to help you people. here is a spreadsheet if you want to fix any collisions.