From the apple tech specs page for the TB 27":
Height: 19.35 inches (49.1 cm)
Width: 25.7 inches (65 cm)
Depth (with stand): 8.15 inches (20.7 cm)
Weight: 23.5 pounds (10.8 kg)
I measured my 27"s width (mini-displayport model but I don't thing that matters) and measured the depth of just the monitor and it's approximately 1.25". I say approximately because the back is slightly curved toward toward the center so I had to just eyeball it with a ruler along the edge. I'm mentioning this because of what you said you intend to do so the published depth with its stand is a useless number.
Note, even if the monitor depth itself is about 1.25" the power cable that plugs into it in the back has a stiff rubber color so I would allocate at least 2" for the depth to accommodate it.
Isn't there a local store where you can see one of these monitors?
Update: Sorry I don't have specs on the rounded corners. But FWIW the curve looks about the same circumference as a quarter.
Heh, missed that measurement. Again because of the curved back I had to site mine against a ruler and it measured 15 15/16".
I don't think you are going to find any apple diagram or blueprint showing exact measurement due to proprietary issues (unless they patented it). I know at one point I tried to get apple to tell me even how thick the cover glass was (I don't recall why I was asking that now) and they used "proprietary" as an excuse not to tell me.
As X mentioned, you won't get exact blueprint specs outside of Apple. You will just need to measure it yourself.
However, here is what I have just measured, without the stand.
Width: 25 11/16 inches
Height: 15 5/8 inches
Depth: 2 1/8 inches
The back also has the cables sticking straight out. They are bendable but I wouldn't bend them too far.
Be aware that the bottom of the display has ventilation holes. These displays can get very warm and you should not block the airflow vent holes. Also the internal speakers sound comes out the bottom holes so if you want audio, you will need this part open.
I would strongly recommend you build your wall to have an inch or two extra then install a black plastic or fabric curtain around the display to cover the space.