I am making a FPS and the entire game is based on a school campus. There are about 9 buildings that will make up this school, plus there is the stadium (where a boss fight will take place) and the parking lot, ect. I have made the first 2 buildings (well I'm finishing up the 2nd one anyway). When I go to compile the map it takes forever, yet when I do this with just the first building it takes only 250 seconds or so to compile the whole level (it basicly gets stuck with more than one building). The school is just one floor, and each building has at most 12 classes (then I added in all the extras like desks and chairs, ect.). So my question is should I create the entire school as a whole level since that is the game, or should I do one building per level and use warps to take you to different areas? These buildings aren't huge either, 2 halls and 8 classes. I have grouped groups of desks and lights to speed up the process if that helps any. Thanks for any opnions.
BTW for those of you intersted about my game, it is loosly based off of the Metroid Prime series.

Keep in mind that, if you double the number of blocks used, the map will take 4 times longer to build. Also, avoid using texture scales of less than 0.25. For faster builds of simple levels, disable light and visibility calculations on the map compiler options. If this doesn't work, use models instead for the small decals (like desks and doors) as they build instantly. You can use blocks for the exterior walls and for walls that block view of other objects.

You could turn them into pre-compiled level entities, or models. Warping is another option, but not so great if you want to be able to see the other buildings.

If you go with map entities or models, LOD them so that they have no insides when you are outside of them.

For more information, check the manual.

Well in case this helps, I am using grouped prefabs for the desks, chairs, and other things like that.

I think groups won't work for the building, that's only to make editing easier.
The desk, etc.., are they model or level?
If they are level, maybe you can better make map entities of it.
(to make a map entity:
- copy your desk (or something else) in a new file
- build the new file with your desk as a map entity
- to import it in your level, click 'object --> load entity, and set the file type on map entity.)

The desks and other class objects are just some prefabs that come with the program.

Also, on average, how long does it take for a standard level to fully compile?

How long it takes depends on how you build it. With a model-only level, even extremely large and complex levels take but one second to build. If you used snap, you can save more build time. A level with 3000 blocks with snap used would take anywhere from 3 minutes to even a week, depending on the build options. If you didn't use snap, the time could be doubled. I suggest using models for everything you can as, not only do they render extremely fast, but models also give much more flexibility in shape and size, along with far shorter build times. Sure, you can use blocks, especially for walls that block the view of other things, but with yet another trick, though it takes more programming to do so, you can hide invisible objects when not visible.

What about Map-Entities?

Map entities are just as slow as blocks, but the main advantage is that, since they are pre-built maps, levels don't take near as long to build. For something like a desk, a model is a much better option. For walls, blocks are okay, but models can still be used.

OK, the compiler just got finished and I get an error that says "to many edge verticies". What the heck does this mean? Hopefully this is causing the large compiling times, so that when I fix it the time won't be insanly long.