Are you going to be residing in this newly constructed grow room? Or you just looking for a small place to rent just for growing?
Since we are already past the idea of NOT growing with this friend of yours, lets try to help you decide whats the best decision for you.
So you cannot grow where you are living now..are you paying rent? If so can you afford to rent/lease another place?
If so, then a 1 bedroom would be good. Why get a 3 bedroom when your only interest will be with one room.
Ive also seen some nice setups with studio flats and converting the bath tube into a flood n drain holding more then 30 plants in a SOG style setup under 2 1000 w lamps.
Outdoor season is picking up, Its not too late to throw some babies out. You wont get 8ft tree's but they will turn out good. This will give you something to grow for the next few months, and then give you time to organize a well thought out plan for indoo growing.
are your intentions just for personal use, or do you wanna make enough back to break even or pay the bills?