I started a new game, used /cheat to give myself all technologies and infinite resources, and tried to build a rocket silo in my main factory building:

"Rocket silo can't be built on this surface. The Ceiling is too low." (Presumably this error is from Factorissimo.)

I haven't tried to build a silo in a full game after normal progression yet, but I doubt if it would work...

I looked into this some more; it's because I'm using mods that require Space Age features, like the Stack Inserters mod. There's probably nothing for you to do in your mod; at some point I'll report the issue in Factorissimo.