It varies from tent to tent. Different manufacturers will position light braces and openings for intake and exhaust wherever best fits the particular design.
If building your own, you could use PVC pies and joints for the framework, and some blackout poly/panda film for your walls.
Exhaust should be at the top of your tent, Intake at the bottom...
It is generally all up to you to make it as customized as you wish...
For your pictures, Check out
this GOOGLE search.
A no brainer, and probably is the best archive of images available online.