How do you guys take those amazing build screen grabs?

If you are sharing your builds on the Gallery you really should be going into Live Mode to test your builds anyway. You can then simply time your testing with the time of day for taking pictures.

I send my test Sim jogging and once he's out the way and no-one else is in the way, I pause the game to take my shots. If I have to use a family to test then I send them all to the park area in the neighbourhood.