A majority of my income on my 1099 are for job materials, but when I try to enter them as my expense, it does not deduct 100%-am I entering them in the right place?

I am a plumbing contractor, and most of my 1099 "income" is actually the cost of materials, which I have already paid taxes on and do not mark up for my customer. Therefore, the customer is basically "reimbursing" me for these costs- it is not income.  I've tried to enter these as expenses, but it doesn't deduct them 100%- I don't know if I am entering them in the right place.(I am filing for 2017)