It's a DIY job.
You may only need to fix the roof if other part of the shed is still in good condition.
BTW, what kind of material your shed built from?
The plastic one has limited size and is too expensive.
The metal one will rust over the time.
I personally prefer to build a wooden shed by yourself.
You can buy the material (mainly 2x4s and some boards) from Home Depot or Rona.
You may choose the base size as 4'x6', 6'x6', 6'x8' or 8'x8' and height as 6' to avoid many cutting jobs.
The cost is about 1/3 of buying a wooden set which you still have to install it yourself anyway.
BTW, I've built one myself about 10 years ago. It's still in very good condition.
Because I am not able to build it by myself:blowzy:, the only choice left is buying a plastic/resin one, though the price is ridiculous. I wish I were handy.