My new studio (a garage conversion) is almost complete - though it will be a minimalist studio comprising of.... Apple iMac 20 2.16Ghz Intel Duo core processor. 3GB memory. 256MB Graphics card. 250GB hard drive. Construction of this studio was fairly straightforward in that the garage was already integral to the house and structurally sound for battening and plasterboarding using 12mm acoustic board with 50mm rockwool in between battens on the walls and 100mm rockwool in the ceiling joists. I also added a layer of rubber membrane for added sound deadening to the room above. The floor is carpeted and all that is left to do is add acoustic treatment to remove unwanted reflections - but not too much! Early tests have indicated that I won't be monitoring too loudly at night, but the extra effort has made a small difference in attenuating the sound from the room. At least I won't have to monitor on headphones!
Not to say though that a trip to a really pro studio has gone out the window.