The size of the roof overhang you choose depends largely on the style of your shed s roof.
Flat roof without overhang.
On buildings where the top of windows are close to the top of the building wall there may be insufficient space to construct an overhanging roof eave without blocking the windows.
This is something you can request from your roofing contractor as you plan your roof replacement.
The overhangs on the gable ends were cut off rigid insulation added to the top photograph 6 and then the overhangs rebuilt as box beams photograph 7.
Most sources i ve read attribute the use of hip roofs with no overhang primarily for withstanding wind especially effective with hip roof usage 100 mph winds etc.
Rafter extensions would need to be added onto your existing rafters.
Gable roofs even with no overhang are at a disadvantage in high winds.
That said overhangs can extend as far as 2 without the need for external supports.
Then the box beams were trimmed out photograph 8 and a double frieze board installed to hide the increase in roof thickness without requiring redoing the gable end siding photograph 9.
There is no good way to make that last.
I can understand not wanting one with a flat roof but the sloped roof without overhang i never understood.
The good news is that a roof overhang can usually be added without having to change the main structure of your roof which is a more expensive and all encompassing job.
This is probably the most costly solution to an un vented no overhang roof design and is practical only in cases where the building is being modified for other reasons.