If you're building a Kamm with the top up, use that. If you're building one to replace the soft top (Miata hardtop style) use an image with the top down. If the top is down you'll have to use the windshield and roll bar as a starting point and
plot your own roof apex.
Here is a more realistic side view.
With a (soft?) top, for head room reference.
Be wary of frontal area when designing the roof.