Need help modeling office tenant rollovers

I'm kind of new to modeling rent rolls for office tenants in excel and want to build a model that shows cash flows on a yearly basis, but with a year that starts in June - May. I want to use as few rows as possible and want my Base Rental Income line (for each tenant) to have a formula that accounts for both in-place lease income as well as whatever the new rent will be once the in-place lease expires. For example, if lease expires in August, I want to allocate for three months of in-place collection and 9 months of collecting rent at new rents. I'm assuming all tenants leave after expiry so that rents can be raised to market. 

My initial though was to use a Yearfrac formula to appropriately separate in-place rent & new rent, but I'm struggling to incorporate the new rent into the formula. 

Anyone have any inputs on this? Would be eternally grateful!