Listening Room Dimensions... I'm building one and need your help

Give Art Noxon at ASC a call. He'll work with you all the way through the build. I've been in a room constructed using his wall products (that of Audiogoner folkfreak), and it was incredible.

As an exercise consider a contemporary performance Hall and note the 
design features.
Expanding from front to rear and overhead dimensions are expansive.
Avoid parallel surfaces and plan ahead for treatment.

Early on in a project like this is when the most far-reaching decisions are made, and it is when your knowledge and experience are the least. So this is arguably when you will benefit the most from the services of a professional. I am a reasonably educated amateur (been building speakers for a variety of applications for over forty years), yet what a real professional acoustician can do leaves me in the dust.

I highly recommend Jeff Hedback of Hedback Designed Acoustics, he is a multi-award-winning studio designer and also does superb home audio room designs and acoustic treatments, with budget and decor very much in mind. Jeff has extensive expertise in what you are trying to accomplish at BOTH ends of your room, AND he is still affordable. Bring him in as early as you can in the process and it will be the best investment you could possibly make.

Just to give you a taste, here is an article Jeff wrote for GIK Acoustics. It does not delve into room design itself but that is likewise an area where he has world-class expertise:
https://www.gikacoustics.com/diffusion-by-jeff-hedback/

Duke