What is the maximum z-level I can reach?

I have had a really excellent idea for a small megaproject (a kiloproject?), but I don't think I can see enough z-levels to build the whole thing. It would need 20-30 above the ground, and IIRC I can only see about 10. So, is there actually a hard ceiling (as it were) that I may run into, or will DF add levels as necessary so I can build as high as I care to?

Incidentally, my kiloproject is a red (bauxite) pyramid, topped with a black (obsidian) inverted pyramid, and maybe some stupid magma tricks. My nobledwarves will be so pleased.

I believe the ceiling is capped at 10 z-levels above the highest ground level on the map.

Basically, you want to look for an embark site that has a peak on it - you can flatten the mountain downwards to get enough "headroom" for your project.