It would be like replacing a good slate roof with shingle..

They mentioned to us about roof damage and reminded us about the shingles that flew off during Hurricane Irma.

Then every once in a while he would reply about some problem he had, he apologized and said they would start on Monday.When I asked for my money back, he then told me that he had bought all the shingles, so he couldn't refund all my monies. 

According to the inspection report, there are 3-4 layers of existing shingles under the newly installed roof.

Is that based on the exact house size, the house size plus 10% for waste or the amount of shingles used.I haven't had to hire a roofer in a while, but when I have in the past it's always been priced based on the size of the house. 

After purchase, The roof leaks, I contacted the village to get the information of the contractor and  they informed me the roof did not pass inspection and the roof ridge lines are collapsing and certain areas of the roof need new decking and the shingles were not installed with underlayment.  

I added it after a tenant complained about the roofing company using "his electricity" to re-shingle the house. 

OR $3,000, to overlay new shingles on top of old shingles. 

Find a company that has a large crew and can do it in a day, assuming it's asphalt shingles it won't take that long2.

Once I learned that end I saved a lot of money from needing to pay a technician to replace exhaust fan motors of relays.You can learn how to do roofs by reading the wrapping paper on any bundle of shingles, or you might be able to find an article called "your roof, for heaven's sake" which was published about 25 years ago by a California property owners' association.