Building a house

If you're married have your better half sign off on absolutely everything you are going to do beforehand. My mistake was getting her to sign off on this being my room alone to do with what I wanted. Thirty years later complaints were still coming in, fortunately only sporadically.

Plan  room entrances and walkways carefully so as to not interfere with speaker placement. I messed up on this and now have to place speakers much closer to the walls than would be ideal, and had to avoid ported speakers due to the wall's proximity.

Another small issue is not to have a couch for your prime listening spot that has the crack between it's cushions exactly where you need to sit. That alone will provide a daily annoyance that can last you years on end. 
Plan the rooms decor to go with your speakers, or vice versa. That helps on the marital front too.

You've gotten a lot of good suggestions on this thread so far.. Good luck with the construction. 

Mike

In case it wasn't obvious, the electrical outlets close to ceiling are for home-theater/surround-sound wireless speakers.

HVAC guys don’t like sealed rooms. Air in needs an air out.

Like me you are really fortunate to be able to start from zero with your listening room.  I had been doing hi-fi for 50 years before my chance came.
There are already some great suggestions above, so I won't repeat any of those..

My room is in the basement.  As I've said in other posts this gives real advantage by enabling all equipment to be in hard contact with the floor/ground so it cannot move or vibrate, causing distortion of the signal and corruption of the soundstage.  Ensure the mass loading is maximised by using heavy support materials.

A basement siting also removes the temptation to include windows.  Glass is about the hardest most reflective substance there is and can reflect sound waves behind curtains and blinds.  Concert halls and recording studios don't have windows.

With an empty page, acoustic design starts from scratch.  So there is every chance to get it exactly right.  There is a temptation to over-damp with thick layers of padding on the walls and thick rugs. Even ceiling treatment.  This is not the best way to go, some sound reflection is required, to create a realistic soundstage and room boundaries.  So I very strongly recommend paying for an acoustician with relevant expertise and experience to advise; the price will be very small relative to the overall construction cost.

Prepare for a shock.  You will have a bigger sound quality upgrade than an order of magnitude more expenditure on equipment, wires, tweaks, the lot.

AVOID a windowless basement!