My answer to the OP was to use rubber rather than felt, as an off cut is a similar price and it's more durable. Steel will perhaps be up to double the price of rubber, based on what i turned up when pricing a job recently and they're a bit more ungainly (for delivery purposes), coming in 3m x 1m sections in 0.5 to 0.7 mm thicknesses, and need better tooling to work with. Not sure I'd go for the 1.3m x 0.5m packs of 0.25mm sheets that seem to flood eBay/amazon
If the OP were to source from a manufacturer of the steel sheets, rather than a reseller, he would be able to order what ever length he wants, ready to fit, and at less cost, with no waste, ready sized to fit. Alternatively, if the OP needs to really save money - FB market always has lots of reclaimed sheets for sale, but they would need cutting to size. The sheet is very easy to cut, the manufacturers suggested method is to use a scissor action cut - basically tin snips. The scissor action, they suggest, smears the galv coating over the cut edge, to protect it from rust. I had to cut a corner off, and there is no sign of the cut edge rusting.
The sheet, begins life as a roll of steel, before entering the folding machine, and they just preset how long they want the lengths. My garage roofing sheet layout, worked fine with standard length sheets, which could be adjusted to match, because they overlapped. The workshop roof, I used full length sheets, designing the roof to fit the standard sheet lengths. When it came to the already built summerhouse, I ordered the panels to custom size, direct from a manufacturer.
The latter, used one single section sheet, from apex, to gutter, and was actually cheaper doing it using custom sized sheets, than buying standard sheets, from local suppliers. I just indicated the colour finish, the length, and the number I wanted, and they quoted me the cost, delivered. I posted the details of the company on here around 2 - 3 years ago.