I made mine with the same lumber used for the siding, rough cut 1x8's. The inside is horizontal 1x8's butted together. The outside is vertical board and batten to match the siding and there is a sheet of tyvek in-between to block the wind from blowing thru the cracks. Where the doors meet there is a batten overlapping to seal that junction. My doors are on the sides under the eaves so there isn't a problem with rain coming in the top like there could be with the normal placement on the end wall. The doors are wide enough that when closed they still reach to the first batten on the wall to give a good seal on the sides. Wish I had the time and patience to document my project like some of the other posters. I can send pictures of the doors if your interested.
Brian
Brian