Using a legacy version of SketchUp Make, I fully recreated my room in the 3D space. It was a time consuming process that has taken a few hours but using a digital tape and a lot of time I have a (mostly) accurate digital room I can work with. I plan on using this for another project in both the bathroom and room next to mine so I did more than needed for this single room.
I used a magnet to find all the screws/studs holding up the existing drywall in the room. I plan to take take those off the wall in the next step anyway. I also marked my outlets, windows, vents and any other necessary items to make this as accurate as possible. Of course once all the wall are off I can re-measure as needed and correct it if I really want to be a perfectionist.
Next I started the rough design of building a room within a room. I have decided I'm going to be building an inside-out room as I'm convinced I'll get the best results for the lowest cost. Originally I had leaned towards iso clips since it would have also given me the most space, but in the end I was swayed away from it.
Also, I worked with another member in the JohnSayers studio building forum and created a MSM Transmission Loss Calculator spreadsheet. If building your own studio is something you plan to tackle, perhaps it will come in handy for you as well.