hey bro,
first of all converting your room into a jamming studio is a very expensive procedure. you'll be required to get clearance with hdb (if u're staying in a hdb apartment) because the sound proofing material used is flammable.
you'll probably need a mixer, your drumset, 2 guitar amps, a bass amp, keyboard amp (if needed), vocal amps, and monitors if you're hardcore enough.
soundproofing your room will run you back by almost 10k, because they'll be building a room within your room, complete with soundproofing and sound absorbant material.
i figure you'll need at least 2-3 power sockets there, and you should do your homework and check with the relevant authorites because im not sure if the amount of electricity your band will consume within the room itself will trip your circuit breaker.
oh yes, and you'll need an air con otherwise you'll all suffocate in there because the door will be shut and there can't be any open windows..