Discounted cash flow for an office tower

An office skyscraper is being put up for sale. How would you value it using a discounted cash flow approach?

Discount projected net operating income plus an exit value. Forecast rents from existing leases and expected renewals, allowing for vacancy, then subtract operating costs, capital expenditure and leasing costs to get yearly cash flow over five to ten years. Add a terminal value (final-year income divided by a market cap rate) and discount at a rate reflecting property risk, then cross-check with comparable sales.