Not only if a tenant goes after you, but if something happens in your personal life (you're at fault in a car accident), your assets are protected.

Life is unpredictable and unexpected repairs/vacancies could really stir some chaos if you try to buy when not ready.P.s.

Next property was an unexpected $5,500 for a furnace and duct work.

If you get a quote on the roof and the comps support your purchase price + the repairs with a little bit more wiggle room in the budget for an unexpected repair or expense then your deal is likely a good start.

You are already at the top of your budget, even if the seller agree to reduce the price, do you have budget for unexpected stuff you find during your repair?  

Finally, expect the unexpected. 

Obviously many costs are unexpected and can be difficult to quantify. 

I recently got into an accident with a driver that has no insurance, and I only have liability coverage.

Or a significant expense unexpectedly pops up (it will happen).

We had some unexpected issues pop up during the rehab that cost us money.