Why do you need people at all? There are lots of photos taken of industrial sites with no people involved. What sort of feeling are you going for? Once you know what feeling you are going for, you can adjust the lighting to support it. If you want to be accurate, might want to go to Google and do an image search for construction sites or something similar to get a feel for what's in a construction site. It looks pretty cool now, would like to see the final version.