Proper Room Dimensions/Designs/Acoustics

I have the chance to build, from ground up, a dedicated listening room. I have spoken with Dennis Foley about the proper design, dimensions etc. Does anyone have any experience either directly or indirectly with him? He designs the room, so all the diffusers/absorbers are built in, instead of using additional stand alone devices.
I cannot give you any experience regarding him but it seems to just make sense to design the room properly from the get go and to have all of the diffusers/absorbers built in. Standalone devices are used when rooms aren't properly designed to start with or are not optimum to begin with. It sounds like a great opportunity and best of luck with it!
Don't know him, but there are many ways to screw up a listening room. I'd take the time to educate myself so you're at least familiar with the basics of room design. I highly recommend reading Premium Home Theater by Earl Geddes. By far the most useful and approachable book on the subject I've found, and the concepts apply to stereo listening rooms as much as Home Theater. After reading it you might be able to design an excellent sounding room yourself and just hire a good contractor to help build it or even do it yourself. This is not a cheap proposition no matter which way you go, so I'd recommend arming yourself with as much info as possible before proceeding. Hope this helps and best of luck.
Don't know him, but I'd agree, there are many ways to screw up a room.

From what I've read the ideal dimensions would be some multiple of 1 x 1.625, with the latter (the "long wall") where the side speakers would be positioned.

Having worked in a few recording studios, the engineers always tell me "no parallel walls".

I moved my audio system down to our family room, creating a "man cave" and pursued multiple upgrades, each one easy to incorporate into the room...until the new sub woofers arrived. The room is roughly 24 x 26 and has all sorts of zones where certain low frequency tones resonate greatly, others where I have big dead spots. I am about 90% to where I'd like to be, thanks to installing bass traps from ATS Acoustics.

Good luck with your project!
@handymann -
I purchased his all in one designs for like $49.

Currently I am building four QRD17 panels out of cherry wood.
Essentially I have a pile of pretty American grown cherry wood ($2000 worth) in 1/2 and 1/4 thickness hiding under a blanket, awaiting time on the CNC router table.

He really seems to know his stuff, I might be totally fooled, but I’m going with my gut on him being a bit of a guru.
One reason I give credence to him is his low frequency absorber using activated charcoal. I have been to the Genolan Caves in New South Wales, and while there they did say that orchestras do come and record in some of the caves, and something about amazing acoustics for recording etc. It was the mirco pores in the limestone apparently...porous like activated charcoal. To some it may seem a leap.
Anyway he uses activated charcoal in his bass absorbers, that do apparently have certification for measurement.

If he’s not the real deal, he aught to go sell used cars, because he sure has me hook, line and sinker.

The plans I purchased were checked out by my friend who is a cabinet maker (his factory is where I did all the wood work) and it aught to build nicely. I plan on buying his activated charcoal and building his bass absorbers as well.

You’re going to build the treatment into the wall frames and floor joists like he shows? I would love to hear that (and do it). He’s not cheap, but then I do believe with him at least, you will get what you paid for.