Been "rolling my own" for years. Of course, with the parts kits drying up, my builds these days are more oriented toward one-off "wonder how this would work out" designs. Latest is a 8x57 AK (yeah, call me nuts!)
So far have built (all semiauto):
AR15 - eh
probably some other stuff I can't recall.
Biggest thing to remember is to make DARN sure there is no way it can be "readily converted to fire full auto". And thats were I have the most fun. Any slob can reweld a receiver and chuck some parts in it - but it takes finesse to come up with a way to make sure full auto parts can in no way be used, and to come up with a way to make it fire from a closed bolt (if applicable).