Automating Monthly Cashflows From Rent Roll

All,

I am new on this forum, and am looking for a solution to an issue I have been trying to solve all week. I am creating an acquisition/development model for the real estate development company I work for, and need a way to automate monthly cashflow based on lease start date/lease end date inputs I enter in. For example - Bob's Cleaners may lease a space for $10 per square foot for 5 years, and have 2 further 5 year extension options at $12 and $15 per square foot respectively. Months 1 - 60 will have one formula =($10 input cell)*(SF input cell), months 61 - 120 will have another formula =($12 input cell)*(SF input cell), and months 121 - 180 formula will equate to =($15 input cell)*(SF input cell). Attached is an image showing the input tab. The goal would be to automate to show a per year total rent figure (off of as many as 50 leases) if possible. Any help would be so greatly appreciated as I am really stumped!

Rent Roll Example.png

Best,

Stephen

Model uploaded.