Pond Boss Forums POND CONSTRUCTION Selecting a site Boat launch and dock construction

If the 2"x4"s are attached upright, you put two nails in at an angle from opposite sides. They only go through the bottom 1/2 to 1/3 of the purlin.

The barn pictured above has purlins every (IIRC) 28" or so, with a 5 foot span between the trusses (center section) or rafters (side sections). Given your purlins will only have to span 2' between trusses, laying them flat should be no problem at all.

I think 4/12 pitch trusses should be fine for your snow load, even if you're in the Lake Michigan snow belt, unless you're putting on gutters. A steel roof sheds snow a lot easier than shingles. 4/12 is not too bad to work on after it ages; roof sheets IME are shipped dripping with a silicon spray-like preservative that is really slippery until it drips/weathers off (it tastes lousy, too). Even if there's no preservative to speak of, they roughen up a little after the galvanized starts to oxidize. The roof above I worked from a roofing ladder suspending by rope from the opposite side of the barn, passed over the crown. But it has a lot bigger span and a lot higher drop (20+' for the center section) than your dock.

Use screws to hold the sheeting down. I used to make good money renailing steel roofs on pole barns after they'd aged a few years.

Are you going to seal off the under side of the trusses with sheeting like the classier dock roofs we've seen pictured here? It'd be nice to have it bird-, bug-, and varmint-proofed. Although the challenge of shooting a raccoon out of ones trusses without holing the roof can be fun.