Steele Garage in suburbia. Here we go.....

Hello all. I come to this forum for HELP! I've been scanning this forum on and off for as good as 2 years now, and trying to design a studio in my head for far longer. I'm constantly amazed at the knowledge on sound floating about around here and am hoping for some serious assistance. So.. as so many before me have said "my wife finally agreed to let me have the whole shed for my studio", now so do I! My ideal end result would be to set this space up with an isolation room for vocals and amps, a room big enough for a 4 piece band to be comfortable in (this would be an occasional rehearsal space for my band), and a nice sounding control room. As I said my band would use this live room as a creative space too. Check out the overhead photo, you can see than the garage is a good 20 meters from and houses. Sound proofing is an issue though, as i'd like to be able to be creative after 8pm, and just not disturb the neighbours at any time really. The foundation is concrete everything else is steel - the walls, the roof, the framing. There is no ceiling ( I would hope to build the ceiling to the shape of the roof, as if it was built flat at the frame it would be too low at 2040mm). There is already power to the garage. I hope to get out of this for under $5000. I'll do a lot of work myself, with help from freinds. Probably the framing i will get a tradesman to do. I will watch for sales on insulation & drywall!! The good thing about this is I have a nice decent size blank canvas - the bad side is i'm on a tight budget like most of everybody, this is basically a tin shed so it's going to seed some work. I'm thinking the best approach is room within a room. Before I get down to the design of the rooms I want to make sure i;m on the right track. And I will start with the outer shell (seems right???). PS all new framing will of course be wood. I have no idea were to start in reagards to the flooring. I would prefer not to float a floor on planks. Currently I think the best way go about it is to start with either: OPTION 1 1) A plastic sheet of membrane against the existing steel framework, then 2 sheets of drywall onto that (horizontal & vertical). 2) stud out from the drywall and fill with insulation (as the insulation is not heavy, do I need an outer frame?) 3) Leave air space, the build the inner wall frame, fill it with insulation then another sheet of drywall with would be the wall of the inside room. OPTION 2 1) Insulated in the steel frame work against the outer steel walls 2) 2 sheets of drywall onto the steel frame 3) leave an airspace then build the room frame 4) Insulate the room frame then put on the drywall that will be the inner wall. How am am going!? Should i slip some sheets of rubber roof matting in there? I apologise for my bad sketchpro'ing! Lets make it happen guys! THANKYOU Anything??? am I on the right track construction-wise?