Hello
While I'm quite familiar with scripting and making armors/weapons/races, I've never created a map. I wanted to make a mod that places Gates of Oblivion in Ald'ruhn, with the Plane of Oblivion being a fake exterior cell like Mournhold. It should be a small-to-medium island surrounded by lava, just like in TES4, but I have no idea about how to make the landmass itself. Is it possible? If not how could I do?
Here's a pic of the modders resource I modified for the http://www.majhost.com/gallery/Frank819/Morrowind/daedric_portal.bmp.

Nope, no landscaping in interior cells. Even ones set to act like exteriors like Mournhold. It can only be done with statics. All the grass you see in Mournhold is built from meshes, not with the landscaping tool.

With that said, there are some tools available which can convert landscape data from an .esp or .esm to a mesh which could be placed in an interior cell. Sounds like that's what you need. So you could convert the Ald-ruhn landscape to a mesh and then place it in your interior cell.

http://morrowind.nexusmods.com/mods/20928/? is the name of the tool I'm thinking of, but maybe there are others which I'm not remembering right now.

I'm sure others will be along to help you out too.

edit: spelling

That sounds exactly what I needed! I'm gonna try it out right away, thanks!
Also, does anyone know how to make sky and weather settings for a fake interior?

Yes, you set it to act like a certain region type. In the same options window where you created the cell. When you select "act like exterior" a drop down menu should be available where you could set it to, say, act like Red Mountain or something.

You're limited to the weather settings shipped with the game though. You can't create custom skies or weather patterns unless you use what people call a http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=8211. And those are imperfect imitations, unfortunately.

Sorry I don't have specifics on the cell creation window. I don't have the CS in front of me.