I'm just now learning SW-Sheet Metal.  If I were so inclined, how would I make a six-sided box out of sheet metal in SW?  I can make a five-sided open box of sheet metal, and obviously the 4 "walls" fold flat...so what to about adding the top? Make the top a separate part and start using assemblies?  If so, how does the top (6th piece) get "welded" to the 4 walls below?