new house - new studio

Due to the need in getting a bigger house were moving to a farm kinda place and have acers(literally) of land to play with. My budget is around the 20 grand (£) mark ( concrete slab exterior walls roof, and sound proofing) i just want to know how much space i would need for a studio like the attached, and what to build the exterior wall out of. I dont need the work done quickly and i'am happy to do most of it myself. Any thoughts? extras that i missed off my band will be using the live room to pratice in. im in the planning stages my band is fairly noisey so would like to be as sound proof as possible. just to clarify i would like to know what realistic dimensions i could use for this and also what i would build the building out of. (the building isnt built yet)