DIY greenhouse: How do I connect and seal the windows?

[theholycow]

I've had the idea, for a long time, to build a greenhouse from discarded windows/glass doors. I've collected a lot of material and there's a couple ads in the Craigslist Free Stuff section right now for more. Footings and framing would be similar to a house or shed, but arranged to fit whatever windows I'm using. I could screw through their frames into the wood to secure the windows/doors to the frame.

How would I join the windows at their edges? For horizontal edges on the roof I can lap them, and for vertical edges on the walls caulk should be fine. What about vertical edges on the roof and horizontal edges on the walls? I guess I could lap the horizontal edges on the walls too but it would look awful. Maybe just caulk them and accept a little bit of leakage in driving rain? I still don't know what to do about vertical edges on the roof.

Edit: Actually, I guess the vertical joints everywhere will have 2x4s under them, so caulk should seal them well. Nevermind, I seem to have worked out the questions. Topic is open for comments and ideas though.