So I was thinking now that I have the basics to modding down I was wondering how hard it would be to make an underwater city (massive ruins much like bioshock) would it be as easy as makeing new land, difficult, impossible, ect.
Thanks for the replys!

Your question is a little vague. Exactly how big would this city be? How many NPCs? Would there be quests? Would there be new weapons, armor, clothing? Would there be new gameplay features? Until we know what you have planned it's nearly impossible to tell you how long it will take or how hard it will be to do.

I like your idea could be hard depends what you find if you get into it. You might be best to have this in the CK threads you might get some pointers about what you can do.

Seperating wet from dry areas wouldn't be too hard you simply teleport to cells with the coc marker above or below water. Filling up and draining air locks not too hard you can use TranslateTo on a WaterREF with some logic to control it, throw some water effects on triggers and that would work pretty well (have a look at the TG water filling dungeon).

Your big problem being able to look out through glass windows that would be where the real work is. First thought maybe the portals that you use to teleport to the wayshrines in Dawnguard.