IMHO, if it was me, I would put off the projector choice until the room is built. Things will then be cheaper and better and there may well be more choice. I don't know the choice of the projectors you are talking, but my experience is that it is cheaper to wait until you get what you want, rather than jump in early and then unnecessarily upgrade. If when the room is finished the ideal projector is still 6 months, year etc away, then buy a cheap projector or one with good resale value (even if you have to mount it temporarily on a table) to tide you over and make the final choice when all the pieces are in place.

I know that alot of custom stuff is made to measure with tight tolerances so this may not be possible, but I am sure that the design can be made to take this into account.

Meridian owner since 1992
Prime & PSU, Focal Elear headphones, Roon (ROCK 8Gi5 NUC), Explorer 1 & 2, F80. 200/203, various Sonos (via Roon).