Brettski,
I have some experience with metal roofs on wooden buildings. The attached picture is of my wife as we put the roof on our home.
The metal is attached to the purlins. It's always screwed on. NEVER nailed. The screws have rubber gaskets on them that you tighten until it starts to bulge. Too tight and you will break the seal. The screws go through the low part of the metal directly into the purlins. You NEVER attach a metal roof through the ridges.
Metal comes in three foot widths, but it's easy to overlap sections in one foot widths. Your supplier will pre-cut it to you in any length you want.
Spacing of your truss's can vary from four feet to 16 feet or more. I like 4 foot centers on my truss's. Your purlins need to span the width of each truss. I like 12 foot pulins and I stagger there ends. Each one up starts on a different truss to tie everything together.
My purlins are on 4 foot centers. Without snow, you can put them further, but snow load and pitch need to be engineered if you do that. I wouldn't. You can put them closer if you like, it's just extra lumber.
With your truss's on 4 ft centers, you can use 2x4's on there flat sides. Further spacing of the trusses will require 2x4's on there edges. It's real easy to attach them on there flats, so that's the way I do it. This also gives you a large surface to attach your metal panels.
I buy my stuff at
www.muellerinc.com here in Texas. I know they are not in your area, but they have a good website with prices that should give you some ideas. Home Depot and Lowes don't sell good metal. If you want to do it once, buy from a metal building supply house.
The main failure point on metal roofs is the screws. Mostly it's from overtightenign them, but cheap screws will fail. They either have inferior rubber gaskets or the metal is crap. Buy quality screws!!!
To keep it simple, build a gable roof. A hip roof might look nicer, but it's more work and the framining is allot more involved.
Have fun,
Eddie
