What is the ideal listening room size?

What would be the ideal dimensions for a listening room? Is the absolute size important, or is it mostly the shape?

Also, what floor, ceiling and wall treatments, or is just plain-old sheetrock acceptable? Budget for this sort of stuff would be very low, so economic suggestions appreciated.

I realize there may be other threads on this, but I wasn't sure what to search on. Also, I'm no acoustical engineer (can barely spell it), and relatively new to this hobby, so the simpler and more basic the suggestions and reasons, the more appreciated! (And no noob flames, please!)

It pays to hire a profesional but the basics are to do a room with a WxHxD ratio of 1 to 1.77 to 1.93.

Helps to have curves instead of corners and to have the ceiling that has a slite pitch. Start at 9 ft. and go up to at least 9.5 at the back of the room.

Cheap wall material that works good is to use MDF instead of sheet rock on the walls.
Check this out:
Here is a great link: http://www.ethanwiner.com/acoustics.html, it will help you understand. Go to this site, download the room mode calculator, and use it to figure out your room size. There are a few "ideal" ratios for room height, width, and length that professional studio designers agree should be used if possible. Three of these ratios, developed by L.W. Sepmeyer, are shown in Table 2.
Height Width Length
1.00 1.14 1.39
1.00 1.28 1.54
1.00 1.60 2.33

Table 2: The ideal room has a ratio of height, width, and length similar to one of these.
I found out a tall ceiling and a large room almost always sounds better, but most rooms are limited to their ceiling height. Example, let's say a room is 8ft. high, using the room mode calculator estimate the other dimensions you feel you can fit in your space and see if they are exemptible ratios in the chart. I came up 8ft. H x 12.6 W x 17.5 L using the mode calculator = H 1.00 W 1.58 L 2.19 as you can see they are acceptable ratios in the chart
Height Width Length
1.00 1.14 1.39
1.00 1.28 1.54
1.00 1.60 2.33
1.00 1.58 2.19 < My example:
Once you get the room built you should still do a sound treatment because even tough you have ideal ratios you are still going to have standing waves and nulls, etc. Here is a link to help you with with room treatment. http://www.realtraps.com/
Awesome! Thank you so much for this info and pointing me in the right direction!

I also found some other threads; I have LOTS of reading ahead!

What a great forum! Thanks again...