It's called cooperative. If I'd like to live in apartment complex, I'd post an ad like "Buy an apartment in a future complex for a low price of X! Move in in only 2 years!". (Cost to build Y, number of apartments Z, X = Y/Z).

And it's not something new. When price is lower than market, people do buy it.

You’ll need a construction cooperative. IDK if those can compete with large construction companies due to the economy of scale. The construction cooperatives were a staple of late Soviet and post-Soviet Russia, but were essentially outlawed later to make way for large construction business and mortgages-backed construction.