Hey, I'm making a city in an interior cell, and I was wondering how I'd go about putting whether and sunlight in. Or, Would I have to make this in an exterior cell? thanks.

Take a good look at Eldergleam Sanctuary or something similar, It's a cave in an exterior cell, so you'll have to make a new worldspace.
I'm currently working on something similar. Take good note of all Eldergleam's settings (region, weather,...).

Are we thehttp://tvtropes.org/pmwiki/pmwiki.php/Main/ThePhantomTollbooth now? It's not as important to know what the weather will be, but whether there will be any weather?