Hi Eric,
Cool an oven builder in Sweden! That's sort of nearly Switzerland. Close-isch, anyway
We'll be able to start a Continental European chapter yet!
About the forms, it depends what kind of oven you're building. A lower dome is better for pizza (Napolitain style), a higher dome (half the diameter in hight) is better for roasting and baking, and still really good for Pizza. Actually, looking at the things people are cooking in their ovens, it doesn't seem to matter much which kind of oven you choose.
For a lower oven you would need to go streighter up for the first couple of courses and then bring in the sides at a steeper angle, in order to have enough floor space. My own oven is shaped like a perfect half sphere (as perfect as possibly anyway), mainly because the idea appealed to me. So for that your idea would work. But basically if you're using forms, you decide what hight and diameter you want, and then draw a nice curve between the two, starting with a right angle at each end.
So how far are you on your oven? Have you got any pictures yet?
Frances