So I have been kicking around the idea of either building a second shop or a larger shop and vacating the one that I am in. If I build a larger shop it will be 180ft x 40ft. I would use 40ft long trusses for the roof. My question is, what would be the largest spacing between trusses I could get away with with a 180ft long x 40ft deep shop? It will not be subject to local code as it will be out of town in the country. Will be going with a metal roof and spray foam on the bottom side.

My second question is would it be necessary to install decking over the trusses to give the metal roof panels a solid base or could I attach the roof metal directly to the trusses? I plan to have a roofer do the install, I am just curious and in research mode at the moment.

Shop will be in the south where temps get high but we still get at least one decent snow every year or two. Shop would be heated and cooled with spray foam insulation on the roof deck and cellulose in the walls.