I don’t know if the amount of people or slamming down the shingles caused it break a support and then it just slowly started getting worse.

Of course, upgrading to higher end materials/shingles will throw that component out of balance. 

Just ran into this in Swissvale 2 weeks ago, but luckily the changes to zoning were easy to prove and the borough found documentation that predated the change (it just happened to not be computerized though, so took digging in old filing cabinets to find). 

Most comp shingle manufacturers provide warranties on their products.

I actually ran across a few insurance companies that wouldn't ensure my first house simply because it had asbestos shingles on the outside which were original.

I can’t even imagine boilers, cast iron pipes, plaster and lathe, asphalt shingles, wood damage, etc. 

I avoid Flat or asphalt shingle roofs, houses with no garages, yards with lawn, split levels (a landing at the main entrance and then you have to go up or down stairs.), houses with less than 3 bedrooms and 2 baths so people stay longer, and multi-Family.

Depending on the location, a new shingle (I'm assuming this is the type of roof you have) roof may last 15-25 years.

Must have ok to newer looking shingles. 

.#3 Contact Local Contractors for Labor PricingCall local Subcontractors and get budget pricing for common repairs on your typical rehab project.For example, call a roofer and ask what their average cost per Square of Architectural Asphalt Shingle Roofing would be on a 1,500 sf house, with a 6/12 pitch.Note: Some contractors will be reluctant to share pricing without seeing the property, but tell them you are just looking for a rough budget number you can use on future projects.#4 Compile Your Prices into a Spreadsheet or Estimating SoftwareOnce you start to get a better understanding of Labor and Material costs you will want to store this data into a spreadsheet or software that you can use to help you streamline the estimating process.The Book on Estimating Rehab Costs comes with a spreadsheet that you can use to help you populate your own database of labor pricing and material pricing.