I am building a 20 by 20 carport. 2 x 6 stick built rafters with a steel roof. The front side will be open With no center support. I have a few left over laminated beams 1 3/4 by 11 78. Q1. Should I use 1 or 2 laminated beams to span that opening. If I need two, would sistering two 10' beams on the back of the 20' beam be structurally sound.