4 Quick Questions: Simple Vocal Booth Construction

Hi, I know everyone's time is precious, so I'll try to be brief. I live in Syracuse, New York USA. I am in the planning stage of building John's vocal booth in my basement. I do voice overs and I'm looking to build a space with good acoustics. I don't care what it looks like. My budget is $1000.00. 1. The basement has cinder block walls and a flat, poured concrete floor. 2. Basement is 8ft underground. That means dirt behind the cinder blocks (so it's pretty sound proof for my needs). The basement is configured in a rectangular layout. 50feet by 20feet. 3. The ceilings are only 7feet 3 inches before you hit the joists. So, I'm going to have to shorten John's design a little to make it fit (His booth has an exterior height of 8 feet). I'm 5'11" tall. 4. I don't need a window. 5. I've read in the forums that a pre-hung, solid door will work just fine. I've studied John's great design and I'm comfortable with the construction (I am skilled in carpentry and electrical). I also feel I have a good grasp of required materials. There are just a few things that I'm not sure about. So, here are my (4) questions: 1. I read in the forums that floating the floor on concrete is not necessary. So, what is recommended to use as the flooring in John's booth? OSB, MDF, sheetrock, gypsum, plywood??? 2. How is the flooring secured to the 2x4 frame. Is it secured to the top of the frame? Or is it secured to the bottom of the frame so its resting right on top of the concrete? From the illustration it looks like it's "set in" and is neither on top nor below the 2x4s, but resting on a lip attached to the inside of the 2x4s. 3. Also, after I lay some carpeting over the flooring is that all that I do? I just let the booth sit in the corner of the basement with no need to secure it to the the concrete floor (that would be great!). 4. My last question and then I'll let you get back to your lives. What are the slats in the interior corners made of? Also, I believe these to be their correct dimensions: 2.5 ft x 3.5 in x .5 in. I thank you for your time and attention! This is a great site. If the answers to these questions are posted somewhere within this forum I apologize for not finding them on my own. I've read a lot, but I might have missed them. Take care, Todd