A tradesmans want 80% deposit before work starts, is this reasonable?

It is quite normal for stairs to be paid for before they are made as a change of mind by client/non paying client etc can leave someone quite a bit out of pocket.Ask your tradesman to explain his up front costs and take it from there.You shouldnt be paying any labour up front though,only the materials/stairs costs.

no way .if pucker firm 20 to 30% max or on first day of work pay for materials bought for your job . if you give 80% they may do a runner with your money !!

80% is a lot. You could siggest using bondpay for peace of mind for both parties

materials only depending on the job .Make sure what the builder is using the money for thow