Indoors

I sort of feel like an idiot for asking...
How would i give an indoor feeling to a TPS...
I can't do it with terran... Is there a certain doodad that im supposed to use?
Or Is there something else i can use as a roof?
Please help!

Just change the global illumination...

A dungeon will have no outside light so all illumination should be global with no notable direction with spot light sources scattered a round the place.
If the dungeon is above ground, then consider having the light shining from where the windows are meant to be but dim it substantially and use special models to create extra illumination when needed.

If you are on the roof, or the place features a courtyard then natural lighting will do.

Look into skyboxes. You want to make a skybox into a unit (IIRC) and have it follow your unit around. I'm assuming you want it for a 3ps or FPS, or maybe a cinematic.

You can use a doodad to create a building, as an example, and use terrain + pathing to manipulate the real feeling of the building.
An example is in this map here.
Play the map and walk around inside the dropship.
He set the unit to ignore height restrictions, and made the unit ignore pathing requirements, then just built a sort of hill under the ship so that your unit walks up in a way it would if it was really using the dropship to walk around in.