I have a Colonial style house. Two stories, with a 2sty foryer. I plan on replacing my front door, which is a single with two side lites, but I'd like to add a straight fixed tansom above it. There is a double-hung window above the door with a little over 4' of clearance. The foyer is 11 1/2' wide. There should be room. The outside has painted redwood lapsiding. It is quite brittle. The inside is just sheetrock. I'm not looking at buying a custom built door, but do want a good quality door like a Anderson, Pella, Marvin or the like. Is this reasonably doable? I know a new header will need to be installed. I know it's a tough DIY job, but for a skilled carpenter can this be done reasonably?