What should I be careful about compared to buying an existing property, and are there any key differences? 

Closed at a title company I Have the deed I own the house I am looking to pay off the existing mortgage that is not mine. 

I know many variables exist, but I am conflicted about whether to build or invest.

I understand that a rental listing will not generate as much as a sale would, but I think a minimal standard should exist (especially since I plan to buy properties in the future).

I still do have a mortgage on that house, so planning on getting those monthly payments to pay existing mortgage.

Hey Daniel,That is great that you have defined your metrics, but as @Ray Hage stated, a turnkey 7.5% cap does not exist in Miami unless you are buying in the really rough parts. $250K a unit is also somewhat realistic in those submarkets, though not impossible.Your best bet is a value-add strategy on something that has significant upside with a high growth submarket.

It’s a market that’s been growing steadily, and I’ve learned quite a bit about the pros and cons of investing in new builds versus existing properties.

You find out what the existing purchase was and multiply by 25% (has to be over $144K)Example: Home bought 2 years ago for $325KEntitlement used/ Entitlement Gurantee = $325K * 25% = $812502.

This is where the tricky part of STR's come into play since no lease exists. 

A new construction loan Might be more difficult to qualify for than an existing structure loan.