metal roofs,cathedral ceilings,insulation and ventalation

I am currently pre-fabbing a 20x24 camp. The trusses are king/queen I beam design 12/9 pitch, and will be open,having a cathedral/barn look with perlins to attach the metal roofing. my question is about how to go about ventalating the roof after insualtion and some kind if interior finish. Are high points in the "waves",about an inch. enough to keep the air moving if I combine this with soffit/ridge vents? If I used a standing seam type of roof ,what then? any thoughts. the cabin will end up in Maine if that is a factor?....any thoughs   I've seen it "rain" in a buddies cabin during the spring melt...................Larry

I would suggest using a double roof system where the purlins have a layer of sheathing (bead board is traditional for the look up from the interior) to protect them and for looks.
On top of this you can use either a water proof membrane with "battens" to form an air trough then build a sandwich of three layers of foam insulation with a second layer of sheathing, all screwed together via the battens prior to putting on the exterior roofing material(s).

Thanks for the response. there will be some type of finish on the ceiling eventually,but there will be a period when it will have to remain unfinished This project has been done when the cash or materials are available. I actually have been doing pretty good. Here,in CT where I live and being in the construction trade, I actually have very little cash into this project (minus the 1000 foot commercial space I rent for a shop) The roof and the rest of the T1-11 are the last big expenses. even the kitchen cabinets,doors,windows and interior ship lap knotty pine for interior finish are on hand. At the job ive been on,the large equipment comes crated in near No.1 pine from Sweden,this is window trim,door trim and baseboard.......stuff the comes in 4x8 sheets,tough to come buy and as a rule...if it is wood and 4x8 sheet...its $30 a sheet. i'm gonna have to get real creative for the open cieling finish (no sheet rock)  I have been collecting all sorts of odds and ends for my future off grid existence,from heavier gauge wiring for my battery bank to blue 55 gal plastic barrels to Permanent magnet motors,solar cells,ect I have all the materials for my RSM heater and a great little antique wood stove that someone threw out to the curb for the mean time I wish I knew how to post photos from my cell phone,got a lot of good photos     wow talk about a ramble...Larry