I had a small drum room a long time ago .. It was all Concrete walls and floor. I ended up using 4" of Acoustic foam over the kit, not the whole ceiling , {it's what I had at the time. 703 is much better}, and I set office dividers in 2 of the corners, from bottom to top with pink wall insulation behind them.I left the other wall's and corners bare. I loved that room. It was very live but the nasty slap/flutter was killed off. The only rug was a small one for the kit so it wouldn't slide. .. Small room's can be nice.. I would also play things back through a PA speaker in there and mic the room for a reverb sound.
Ivan.............................
EDT: It's worth pointing out that before I treated the room, I used it for some drum sounds and they were, interesting?. They didn't suck. It's just that I was forced into a "Reverb" sound that didn't work for everything. After treatment {of the room I mean
} I could get a deader sound...ie. the room was more versatile..