Trust me, it wasn't easy.
I finally ended up with something that is symmetrical, uses stock windows, and has structural members that are close enough together to handle the load on the roof. And as it turns out, it's almost all glass. Ten windows and a door. And it's tight-- I don't have a whole lot of wiggle room. I might look into the next size down for windows, but these almost exactly match the door width. And I have to admit that a mostly-glass porch is a kind of a nifty idea.
I don't have the height of the windows yet, but that's not as critical. I have some leeway in the design, and the stock windows come in enough varying heights to make it unlikely I can't find something.
Next I have to work on the elevation drawings.