It is becoming increasingly common for Homebuy schemes to start with a lower rent as % value, a discount in early years, then creep up to a higher %. You can use the voids patterns in M3Pamwin to model this. For example, assume that in year 1 you want to charge rent at 1% of retained equity, year 2 2% and year 3 (and subsequently) 3%. Start by putting in rent at 3% of value on the Rents screen. Next, set up a voids pattern as follows: year 1 - 66%, year 2 - 33%, year 3 - 0%.

The percentages will need to be modified slightly if you do actually charge voids on your homebuy units.