This is a really interesting system! The private selection and public reveal is a fun way to take advantage of the unpredictability of players -- which is something I always like to see.
Favourite details: The Outright Leader bonus mechanic is a fun way to make the letters matter in-play (not just at the end!), which I definitely appreciate. I also like the semi-competitive structure, which I fell like goes a long way to providing intrigue while also obligating teamwork.
Would be nice to have: A few more narrative prompts? Right now, the game is right on the edge of board game and RPG, for me. I think that's a fun place to play in, but it might be nice to have a couple more springboards to tell the story of the structure being built -- the game is pretty mechanical as it stands.
But yeah! Big props for the innovative play system, and the unique theme too. Cool stuff.