The sales price of the roof and any other assets you are depreciating is zero.
Thats wrong. If you make the sales price of other assets zero, then the depreciation on those assets is included in the capital gains, and is taxed at the capital gains tax rate. If you sold the property at a gain, you need to show a gain on every asset that is "at least" $1 more than the cost basis of the asset. That is the only way the depreciation will be correctly recaptured and taxed at the ordinary income tax rate, instead of the capital gains tax rate.
