All right, I'm about 60% done with building a building model out of wood, carboard, and chicken wire. I all ready now how I'm going to blow it up, but now, I need it to look life size and not like its sitting in someone's garage.

Should I put a blue/green screen behind it? I hesitate to do that because when I key it out I'm afraid the smoke will screw up the keying.
Or should a blow up a picture of the night sky, staple it to wood nice and flat and put it as a backdrop? (Then light accordingly of course).

The explosion is going to have a WHOLE lot of smoke, so I'm really not sure a blue/green screen will work.

doing it outside would be best.

Run some tests keying out smoke. Sometimes it works well, other times, not as well.

i wuld just take a picture of the background i want and blow it up to size like u said. o and how r u blowin it up?

I'm taking model rocket engines, unwrapping them and connecting the burning stuff with a fuse. Then I'll get a friecracker or two and light them all simultaneously.

I like explosions

How about trying facke smoke instead of filming it? Try this website...it has smoke that can be keyed out

http://www.detonationfilms.com/free_stuff.htm

sounds like an awesome explosion technique, o and i love explosions too!