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!