Best Audio Isolation Set Up

Those shields are not worth the money you spend on them in my experience.

Get a couple of those free standing isolation walls you use for cubicles instead. A cubible is actually a nice place for sound recording if you can get it into a room where the door can be closed.

If you can, carpet the floor. Get a mixing unit with a noise gate to take out the background noise from the breaks and pauses you put in your speech. The noise gate makes a huge difference in my experience. Now you are suddenly recording way better audio than you used to. 

Find a room in a part of the building where ladies in high heels are not likely to walk by on compact flooring outside. The Click Clack travels through any material known to mankind and right into your sound recording.

In our company the recording room doubles as meeting room, except it has a half-cubicle in one corner with a dedicated recording setup, and wall to wall carpeting. It has ventilation and isn't particularly sound proofed, but it works very fine.