My question then is, “is there a way I can work out a rough estimate of how much I can borrow when analysing a commercial property deal?”

Mark,

each commerial deal is different. Most commercial lenders if not all will lend no more than 10% down. Depending on the type of property will depend on the commercial lenders guidelines.

Commercial is a different animal than residential. You first need to define the type of commercial property you are interested in purchasing. Then we can begin looking at rough estimates.