I follow Small Car Garage on FB and he just released some free images that he uses for taking photos but they can also work for buildings on your track etc.
If you want to check it out, here's the link to the free PDF download
It's a great way to add buildings quickly for backgrounds. I did something similar with my first building - I printed out a couple pages and stuck it to a small cardboard box. Looks real enough as the camera pans past it during a race, although now most of the buildings I'll be making will be designed for close ups so will be building them more detailed than that in general, I will still use stuff like that for ones right at the back to add depth