How do you get in contact with new contractors when trying to start your own cleaning business?

Commercial or residential ?

Home builders for new home construction cleaning

I would drive around to new building sites, visit the site office and go from there. I know a couple of people who do this and actually is a good way of getting in on the ground floor for residential cleaning. I am assuming you mean after all the workers have left a home and it is almost ready ocupancy, then a cleaning team goes in and clean up the debris, etc.