Congratulations on you're new project & I'm sure everyone here is jealous that you are starting with a blank slate. I'm not sure how deep a dive you want to make on the room but here are a couple of thoughts.
Number one would be to make sure that you don't wind up with a floating floor in the construction plans. This will cause all kinds of reverb problems that are hard to compensate. Something solid below or a lower floor is preferable. I would put down a hard wood floor and then cover with area rugs to taste to optimize SQ. This gives you flexibility and you will be able to make adjustments as different sounding equipment inevitably comes and goes.
Take care where the room's windows and doors will be located.
Have the electrician put all of the room's wall outlets on their own dedicated circuit. 15amp should be fine.
Find a Vicaoustic dealer and have them do an acoustic room rendering for acoustic paneling. They will computer model the optimal absorption/reflection that will make the room sound as well as possible. I did this and it's the best audio money I've ever spent. Good luck and cheers.