This is getting a little confusing , can't you just post a pic and say how wide the overhang is, how it's formed, and the length of the gutter run.
I have never had a problem fixing gutters on a tin sheet roof with wide overhang so can't really see this being much different.
I like the banding idea because it saves me having to fit an offcut. 600mm along sounds better than 1 meter apart. The shed is a little exposed to the south west for my liking.
Trouble is the guttering will slide about in the sling of the banding. The clips are cheap, 82pence each. I would need about £10 worth.
My main concern is fitting the off cut to the underside of the roof so that it's sturdy. The roof construction is 2x4 with plywood paneling.
I suppose I should go and inspect the half round brackets and see what depth I'll need to make the offcuts https://www.toolstation.com/112mm-half-round-fascia-bracket/p22015
Alternatively I could fit offcuts at either end of the shed and run a fascia and then fit brackets directly onto it. Probably easier and more labour saving.
my thoughts for a cheap job
68mm drain pipe cut in half [band saw]
2x2 treated screwed under lip full length 20mm back from the felt
drill a hole through the half drain pipe both sides 10mm from the top edge
90-100mm screw into the holes both sides about every 5-600mm along its length
Your first illustration is the way I do it but with angle cut on the top equal to the slope of the roof so front edge where bracket fits is vertical
To fix the wood to the underside,bore holes a bit larger than fixing screw head size to sink it deep enough to use a shorter screw
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