Yep, height is the big issue, I think. There probably won't be standing headroom under the doors unless they open well above horizontal, when it will be very hard to make them not dump rain water into the gap between the door and body. Opening high also means they don't stick out as far, so there's less space made.
Even using radiused bottom corners, I expect at some stage someone will walk into the open door edge at eye height - ouch.
True gull-wing doors - that is ones where the opening extends right into the roof - don't have these problems, except for sticking out less, but they sure are tricky to build.
Dan's beautiful Roswell has upward-opening curved doors with internal hinges to look good. But that means there are hinge arms, like giant C-cramps, that stick into the body when the door is shut, just waiting to crack your head on.
