If the roof was not completed "and" placed in service on or before Dec 31, 2019 then you have absolutely nothing to report concerning it, on your 2019 tax return. Not one penny.
Just for clarification, what you spend on the roof is not an expense. The roof is an asset that must be depreciated over time. Being this is for a commercial business, it gets depreciated over 39 years and depreciation does not start until the asset is placed "in service". That can't happen until the roof is completed.
Your "down payment" is not a deduction on any tax return in any way, shape or form. It will be part of your cost basis when you enter it in the business assets section of your 2020 tax return when you complete that return next year, in 2021.
