Depending on the cycle, the cap rate may fluctuate percentage or so. 

IN Minnesota it is a percentage of the rent.I would do late fee's after the 3rd.. not the 5th,If all their names are on the lease legally they each CAN submit a payment,, and you have to accept.  

Is there a percentage that I should use.

If I was to have a brokerage I would definitely expect a percentage! 

The cap rate percentage formula is: Net Operating Income/Gross Purchase Price (x100).As has been written, not normally the used for SFR's.Jack Edgar jr almost got it right, until he wrote: "Divide the remaining money over your equity and you're left with a cap/% return" (But, he may have been referring to "Cash-on-Cash" return, which will vary for any given investor depending on how much deposit they put up)!

Yes, my personal loan rate may be a higher percentage but if you look at all the figures I still come out ahead: short term payoff in 5 years vs 30 years, no closing costs, no hassles if I want to borrow against the property for more money (my unsecured loan is not attached to the property).

Percentage rules often fail people.

A common way is to do a weekly payment based on the percentage of the work done.

I usually break expenses between monthly expenses and what I call "percentage expenses" - percentages are usually taken off of your monthly income as a percentage (probably obvious from the name...). 

What percentage of growth are you basing that on?