Here is one of my many unfinished projects that I will hopefully complete. My idea for this core map was to make something that looks less like a Halo map, but something that could have been in the future, and isn't a simulation revolving around combat. I decided to design a construction map with as much realism as possible. Unfortunately, my crane truck does look more futuristic than I would like it to, but that can still be changed. My biggest challenge with this map was to make the space playable, which is still a hard challenge, because a construction site is mainly one completely open area, and a few extremely close quarters situations. For this map in particular, I wanted focus on the exterior, which creates a single atrium style.
As far as the wide open space issue you mentioned goes, you could utilize piles or stacks of materials. Or maybe have skeletons of the big building strewn about and have them look like the crane truck is piecing them together? Don't be afraid to think outside the ring