It depends on the metal and setup of your replacement pipe. I've heard two homemade versions, one 2.0litre 8 valve (Shug) and a 2.0litre 16 valve (Jason77).
Shugs is thick stainless steel and accentuates that 8 valve rasp. Sounds really nice and not any louder really.
Jasons I think was not Stainless and possibly a bit thinner guage. Again no louder, but his car ended up with a resonance at about 4500rpm which sounded like a high pitched "Zing". I personally thought it sounded OK, but J didn't like it, so put the cat back on.