Soundproofing is not an all or nothing thing. It's a matter of degree. Some solutions block a lot of sound, some less, some even less, all along the spectrum. How loud you can get away with depends on the context. What I'm saying is, think about your overall situation. How loud do you have to play your instruments? What time of day do you want to record? What rooms are adjacent to who and what neighbors might get pissed off? Etc. And it's hard to quantify how well a DIY booth will work in a given setting. Use trial and error. But go by principles. You want absorptive material and the more layers with air between them, the better. You might be able to slap together a dirt cheap apparatus that does enough for what you need. But check. Stand outside while someone else goes in and plays. If it's still too loud, adjust the design.