I accidentially missed the last upgrade of the titan research. Was still able to build the forge and start construction, which was halted at 75%. As i had no idea what was wrong i restarted construction and even rebuild the forge on another planet to track down the issue before i realized it was the msising research. Before this I thought I need all levels completed before I can start building the ship at all. So I'd suggest some description or warning that tells the players that they can start building the titan with less than 100% research but production will then halt until all research is done.

Also, how about constructing the titan in steps (like the incremental starbase upgrades) - if you can research it in steps, why not build it this way? So you can build a part when you got like 2500 gold, not the whole 10k.