I bought a pent-roofed garden shed when we move into a newly built house in 1991. No time to construct a shed back then. It was roofed with mineral felt and underfelt. By 2000, the roof was leaking as the felt had degraded over the years due to snow and ice in winter, so I re-felted it. At the same time, I built a workshop in 2000 and decided to use an apex roof, which I 'tiled' with felt shingles, (from Wickes) and flash-band along the ridge. 21 year on, it's still as good as new, and the storage space in the rafters for lengths of timber etc has been really useful.
In 2013, the felt on the pent-roofed garden shed began to leak once more, so rather than re-felt it yet again, I decided to convert it to an apex roof, making trusses from B&Q 'CLS' timber, which you can self-select to ensure it's not bowed and is fairly knot free. As with the workshop, I used felt shingles (from Wickes) to clad the roof. Again, the space in the rafters has proved very useful and the roof is vey sound. Some pics attached. Hope that's of interest.
Pic 1: The apex roofed workshop, and pent roofed shed as it was, prior to conversion to an apex roof..
Pic 2: The apex roof trusses and ridge I prefabricated in my garage.
Pic 3: Pent roof removed and apex roof trusses fitted.
Pic 4: Inside view before trusses were clad with T&G boards, part salvaged from the pent roof.
Pic 5: The roof clad with T&G boards.
Pic 6: The finished roof.
Pic 7: Taken today - the workshop is 21 years old, and the apex roof on the garden shed will be ten years old in Feb next year.
Pic 8: I've included that to show the moisture content of B&Q CLS kiln-dried timber in Feb 2013. Just 11%. Excellent stuff. ('CLS means 'Canadian Lumber Stock' but my guess is that it's more likely sourced closer to home. From Kielder maybe?).