I just did this to a barn at a historic house in my town. We were lucky enough to have a pile of old boards on the second floor, but you can probably find a local sawmill from which to buy some 4/4 (one inch) thick boards. If all you can get is pine, I'd go for it and apply several coats of waterproofer/UV protectant. I surface planed these 1" thick boards to 3/4" (left a nice patina), edged them on the jointer, then ran them through the table saw to make the other edge parallel and then ship-lapped them on the table saw as well (so you won't see though the boards when they dry out). The door frame only needed one new frame member. It is just a big square with one horizontal member in the middle. We added small 45 degree blocks at each intersection of the framing members. We also bought 30 pounds of rosehead nails from Tremont Nail (I think) which we will nail the boards with and clinch them over on the indside, as was originally done. This is one of the tightest joints possible, even though it looks amatuerish. We also removed the rail and door hanger/rollers, wire brushed them and applied 3 coats of Rust Reformer, neutralizer (available at the hardwar store). they almost look new! Don't become overwhelmed at this task, its really pretty straightforward. I THINK I've added 3 photos, but I can only see one of them when I preview tghis post. If you can't see them, e-mail me and I'll send them toyou. Good luck, Harry