Cost to replace my roof and the correct way to do it.

Hi There,

I have a roof contractor give me an estimate of roof replacement with 30 years landmark warranty material and flat bitument is 20 years. I have not ideas how and what is the correct way that require for roof replacement.

1)the process is tear off the entire roof to the existing roof deck (flag ship -roof deck) and replace any broken or dry rot.

for Shingle roof, put down the #30 felt paper then shingle on top.

for Flat Roof – torch down rubber then put single ply 80 lbs first and then single ply 100 lbs GTA roof

someone give quote is 13K ,

High end is 23K with synthetic insulate

Need your feed back and information to help me to determine for my roof replacement.

thanks

Lusty