Hmmm... you didn't give us a lot of details about the particualar project, or budget, or how big an area or what exactly you need to light, what kind of scene it is, etc., but sounds like you are looking for very soft even lighting.
You could approach that in a number of ways. The easiest would be a couple of medium-to-large softboxes (Chimera, PhotoFlex, etc.).... either on stands, or hanging. I don't know if money is a factor but if it is a couple of open-face instruments shooting through white umbrellas might also do the job (although the output will not be nearly as controllable).
At any rate, epecially if you are shooting talent (i.e., people) don't forget about backlighting... which should be a hard instrument, not soft (fresnels work well). Some people skimp on the backlight (also known as a rim light or hair light) but often it is the very best way to cut talent out of the background.... and even occassionaly(depending on the setup) it can actually be the brightest single instrument in play. Watch talent standing on stage in a wide shot on a well-lit talk show sometime (Letterman, Leno, etc.). Look at the floor, and you'll see that their main shadow is actually in front of them... just shows how much backlighting they use.
If you can tell us a little more about your needs we can probably narrow down the particulars some....
Fantastic Plastic Entertainment, Inc. fantasticplastic.com
basically we have a room in which we set up a green screen area that is about 12 by 12
with ceilings about 20 feet or so high
i was trying to get a lighting scheme that would provide the initial lighting to spread out the light evenly on the area...specifiaclly giving the green screen a smooth light...
the back light advice is great...
we usually do all of this with a combonation of 5 lights on stands but that cuts into our shooting space (sometimes where the camera should or could be)
so i've been thinking that if the lights were hanging it would open up space.
You have provided no information as to WHY you want "overhead lighting to give a nice spread out light", so proper advice is impossible.
My instrument of choice for overhead wash lighting is the simple scoop, depending on the grid height. If I've got a high grid then I'll use sky pans or space lights. That being said there are a wide variety of wash instruments available, and the actual fixture you use can be anything from a 200w Mini-10 Broad to a Kino-Flo IMAGE 80.
Armed with "hardware" knowledge I feel compelled to tell you the BEST advice you're going to get regarding the angle of light you want. You should NEVER use overhead lighting for anything but "worklight". It is the worst possible angle and will yield the most unflattering light for human faces.