like it's been said, pretty much anything is brandable if you have decent idea and you have enough money. You could pick up the domain "HeCaves" to go with it, but I like "DreamCaves" even better. Unfortunately it's a site that's "under construction" at Network Solutions. Learning that, I'd probably pass on trying to brand futurecaves.
You mentioned builders and housing firms, and as such I have a portfolio of .homes domains. Both future.homes and cave.homes are already registered