G'day
Here is another solution:
http://www.insultec.biz/Insultec is an external reflective insulating paint for protecting roofs and exterior surfaces from heat gain.
The problem I had was that due to increased staff numbers the airconditioning system was not maintaining a comfortable temperature within the workshop. Due to cashflow limitations and the high cost of upgrading the airconditioner I installed a garden sprinkler on the roof as an additional temporary cooling system which worked successfully until the staff numbers increased again.
Insultec was offered to me as a lower cost solution than upgrading my airconditioning system. After the paint was applied the sprinkler was no longer needed and even the air conditioner was not needed to operate at full capacity despite another increase in staff levels.
When the workshop roof was being sprayed I asked that the roof and sunvisor of 2 Bedford CFS vans be sprayed as well. The vans got very hot in summer with radiant heat from the roof affecting the drivers. With the cost of fitting air conditioners being quite high, I considered the paint to be a viable alternative.
After being sprayed, the roof of the vans were cool to touch, even on a hot day, with the only radiant heat coming from the sides. After 15 years, and despite neglect, the appearance of the paintwork on both vans is still very bright and most satisfactory.
The cost of doing the industrial shed was $1500 and they did the vans for free.
It was put on with a pressure pot and was sprayed onto anything that didn't crawl out of their way quick enough.
I have just bought a 4 litre tin of a similar paint at the local Solar Shop and will be doing all of the vans before summer.