My philosophy now is to go only for offices and use low moisture. I have various plans for different clients from 3 months through to 1 year.
I've had big offices in the past of 4000+ sqM, and had formal contracts. Administration and procedures for "emergency" cleanups got out of hand so I've stepped back from that sort of work. But if you want the big jobs, that's the way to go.
I prefer to have a good, personal relationship with the facilities manager, submit a programme and quotation. This works for as long as they like a) your face, b) your charges and c) the quality of your work. Perhaps it may not feel as secure as a contract but it works for me.
Clinics and Doctors' surgeries are my biggest market, followed by offices and a couple of residential care units.
Safe and happy cleaning

Ken