Use of absorptive material like glass fiber or rockwool is not enough to give you the isolation you want. What you need is a combination of mass, absorption and/or diffusion. First, you have to make sure that you use something massive to stop the sound, like gypsum, hardiflex or cement. The thicker or more massive it is, the better. This helps not only in stopping sound but in controlling LF energy as well. Contruct a double faced wall all around. To prevent resonance, put glasswool or rockwool in between (that's where it's used). Caulk all possible areas where sound can flank or seep through. Construct a new ceiling. Again use glass fiber or rockwool inside the new ceiling to prevent resonances. Make sure ceiling is hanging - no short circuit connections with the existing ceiling. You have to use acoustical mounts or hangers for this. Build a floating floor using neoprene mounts. Have the walls sit on this flooring. Tame the acoustics inside the room with absorption and diffusion (Glass fiber and rockwool can be used as absorbers here also). As the space is rather small, you probably can use Hemholtz resonators as LF traps. Put rubber gaskets on doors. If you can put sound locks as entraces, the better.
Kinda complicated? Yes. Not only that. Soundproofing is an expensive exercise. First, the proposed studios must be tied up in a contract for at least 5 years. Sayang kasi. You build, spend money and in a year's time your contract is up. Second, there is really a dire need for the owners to go into this type of spending, i. e., they have projects they can recoup their investments from, and are dead serious about the entire thing (thought about it for a long period of time, in sleepless nights). Think about the expenses.
Now, the room. The room will become smaller once you put all the soundproofing and acoustical treatment in. Thus, the bigger the room, the better. Walls and air gaps would take at least 8 inches all around. Add 2 inches of absorbers, 4 inches of diffusers (8 inches is better), and what do you have? A very cramped room. Incidentally, for the sound to be properly propagated and the room to sound well, you need at least 1500 sq ft. of actual studio space, otherwise you will have lots of modal problems. What about your air conditioning system? Are you using a window type air con? If you are, you do not need to sound proof because the window where you have placed the air conditioning system is typically open. You have the option of using a split type. Is the room to be used for recording as well? Then, the air con system has to be pretty quiet, preferably a ducted system (more expensive).
What about your power supply?
My advice? Do not do things haphazardly. Study your actions and your options well. Do not listen to hearsay. Read on it. Get books, magazines, go over the internet and read everything about soundproofing, acoustics and the studio business. But be very discriminating. Not everything that is written in magazines and on the web is correct.
You can also seek professional help. There are acoustical professionals here in the Philippines. But make sure you look into what they have done. If you like what they've done and their ideas jive with those of yours, you have a team. I have seen a lot of wastage in a lot of facilities around. To correct them will be more expensive than to build a new one. So, take it easy, take your time before making any decision.
Hope this helps. Good luck in your venture.
FWIW