Not the greatest home build 'studio' I've seen, he's making some fundamental acoustic errors. What I would like to see is a frequency response of the finished room, as I can't see how it's going to be particularly smooth. It would look to have insufficient bass trapping (there appears to be nothing in the corners at all) and his ceiling 'cloud' seems to be in the wrong place; it's not at the mirror reflection point from his speakers and should be positioned a lot neared the desk (or made a lot bigger). The rockwool panels on the rear wall could easily have been moved away further from the walls in order to make them more efficient.

As a mixing-only environment, his soundproofing measures are rudimentary but sufficient for the purpose. Had he decided to make it a tracking room as well for drums and electric instruments, he would have a lot of issues.

Ventilation is also an issue in spaces like these, and you really do need forced ventilation running through heavily silenced ducts. In Australia, some form of near-silent air-con would also be a real requirement as well.

There seems to be someone who knows about acoustics commenting on those blogs, but he is being told that it isn't really a studio but a 'creative environment'. That is fine, but it really isn't a blog that tells you how to build a good home studio, just a nice room to work in and should be treated as such. But that does seem a bit of a poor excuse. It could have been made a lot better with not a lot more effort or expenditure.