Bill Tindall, E.Tn.
This is a three part project. The woodworking part is easy. Simple frame and panel construction with mortise and tenon joinery. The scale will add difficulty. Can you straighten 7' lumber perfectly, for example?
How are you going to seal it? It may be a challenge figuring out how to use replacement parts for factory doors to seal this custom door. Then there is the finish question. Unless protected by a porch weathering on a wood door is difficult to design for and maintain. The best solution is to paint it. But if you are going to paint it why make a wood door?