It's tricky to find a good place to set up a studio. If you live in an apartment, then unless you live in a very old building with really thick walls, you might as well forget it, or just record the electronic components of your music at home, monitoring on headphones.
But in a house you have options. One very attractive option is the garage. OK, take a look at your garage. There may be a car in it. The first question that comes to mind is, “Does it need to be?”. For my car, I wouldn't bother. My taste in cars runs to 'big enough, 'fast enough', 'reliable enough', and if a car couldn't stand being left out in the rain it wouldn't be much use to me.
Of course, the car might not be yours, in which case you might have to apply a little influence and negotiation. Parents with cars can be very funny about this though.
However, I'd say that most of the garages I've seen have nothing but junk inside them. So sell the junk on eBay and use the proceeds to buy some soundproofing and acoustic treatment!
The main problem with a garage is that it is generally of very lightweight construction. The walls may be only one course of bricks in thickness, compared to two in a dwelling structure. Also, there probably is no ceiling and the roof is paper thin and full of gaps. It will almost certainly stand directly on the ground so at least there will be no problem with the floor.
Soundproofing consists mainly of providing plenty of mass and plugging all the air leaks. There's more to be said about this elsewhere, but that's the principle. So beef up the walls and add brand new beef to the roof space. You will probably want to seal off the up-and-over door because to continue to use it will take up too much space.
One final advantage of a garage is that once you have finished your studio, no-one knows it's there. The garage looks from outside exactly the way it did before, except there is no car going in and out. This is also useful for getting round zoning or planning requirements, although technically it could still be illegal depending on the jurisdiction in which you live.
Hey, maybe you could even start a garage band!