I know the useful life left on the roof is short, so I am hoping there is some negotiating around that.

Your capex will depend on the age of major things on the property like HVAC and roof, vacancy will depend on the market.  

When talking cap-ex, new-ish roof, new water heater, new central air system.

When talking cap-ex, new-ish roof, new water heater, new central air system.

I undertand the 50% Rule is there to cover vacancies and repairs, but just about everything in the property is new from the roof to the central air, and I don't foresee any major repairs for the foreseeable future.

We have removed and replaced the roof, replaced all ceiling sheet rock and finished, to include replaced all enterior doors to date.  

I’ve seen brand new patios slope back towards the house, joist hangers attached with deck screws instead of nails, brand new roofs that leak, etc. there are a ton of hack builders out there creating problems for whoever buys the houses they build that’s why it’s recommended to hire an independent 3rd party home inspector even for new construction.

The biggest ones being a new roof/windows/HVAC, etc. 

There is not set rule on how long you should wait, but the tenants need to understand that the lease is a you scratch my back (pay rent) and I scratch you back (provide you with a roof).

The Roof, water tank, and HVAC are fairly new.