We designed our greenhouse to match the style of our home. The walls are set on two foot high walls with 2x4 studs ever two feet. Here is an inside shot (my favorite) showing the walls and base.
This one will give you an idea of how the roof looks:
And here is a shot of the outside.
You can just google "Lexan polycarbonate greenhouse material" and probably get several links to see the different types.