I did construction for a summer during college to help with tuition. On top of some valuable life lessons, I was surprised by the manual dexterity of some of the crew. They can dump a ton of bricks one minute and connect the copper strands in a Cat-6 cable the next minute. (I'll assume an all-male crew for simplicity.) If you find they right guy, you can teach him how to handle the camera, lens, tripod and case. Let him know what you're looking for, how much time out of the day to spend, and how to be careful with the gear. The construction day starts early so be sure to clear what kind of light you want, like pre-dawn, golden hour, or high noon.
Camera gear can be expensive... but so can construction gear. If you trust him driving the company truck, on a contract worth X thousands of dollars, it's not a big jump to trust him with $3k worth of additional gear. Check with your insurance company to make sure it's covered. Get a well padded camera bag to keep it safe in the truck's cab or tool box.
For the actual gear, I suggest a T3i with a 17-40mm f/4L lens. The flip screen can be handy for this application. 18 megapixels may be enough for your poster. Going to a 60D or 7D may not be necessary. The 7D is physically stronger and has more weather proofing for a couple hundred more bucks. I'm making some assumptions on what you want in your posters, but f/4 should be fine and saves some money. You're probably not making head and shoulder portaits so the focal length should work too.
Get a Pelican case for the camera and lens. The tripod and ballhead will cost about $150-$250. You have lots of options there.
If you know how you're going to display these posters, that would be helpful. Poster for the side of the trailor or fence? In a convention for future customers?
