Waterproof garden shed roof

Google build watertight roofs and you'll get many DIY and U-Tube videos on how to build a watertight roof - or look up how to build sheds. Most any building will be built waterproof. The leaks come after...The cheapest is rolled tar paper on top of wood sheets.

I just had my flatroof done....they used rubber roofing...will last forever. Home Depot sells it

https://www.permagard.co.uk/advice/waterproofing_a_shed_5_steps_to_keep_your_shed

This is a kinda wide open question. Do you have a plywood shed roof on it now with no covering? If so, how much slope? Too shallow (less than 3/12) and you cannot use shingles.

You can use roll roofing, corrugated fiberglass or steel. There's an asphalt corrugated material called Ondura that makes a nice looking roof, akin to the look of terra cotta tiles. You could cover the whole thing using rubber membrane as an underlayment which will keep the roof from leaking when your great grandchildren take over. Because of the small size of the roof you have a lot of choices, even using copper or cedar shingles.

When I was doing a project like this unless there was a specific look I was going after I would look to local suppliers, asking what they had to offer. Sometimes a broken case or damaged roll of something will work just fine.

If you have more specific questions or care to share a photo of your challenges in this project we would be glad to help as much as we can. Being as we are all remote here and everything.

Here is a video that might help - https://www.youtube.com/watch?v=_UbY2EUDjYs

Corrugated plastic sheets. Comes in green or translucent.