Oh and I have got a carbon monoxide detectorCheers fellers, good advice , I'll angle it up more.
I can access the inside of the stove where the flue will exit , the stove is 120mm box, the top is a lid that will come off so I will probably be able to get a brush up the flue a bit.
I can joint it with a smaller piece of box sleeve, would Gun gum exhaust paste be any use to seal this . The joint would be outside the shed above the angle just to extend the riser, the joints on the stove and first angle will be welded.
Had a chance to play around with it again tonight, cut a square for the flue but didn't weld the flue on yet..fired it up.. the lid is 5mm plate with flat bar welded flush with the stove to keep it in place , there's probably a mil gap all way round so I can lift it on and off, the top of the stove was cut on a decent chop saw, it's square and snug to the lid.just use firerope or fire strip
https://www.ebay.co.uk/itm/FLAT-SEL...389446?hash=item440f5ade06:g:~EAAAOSw6GJZ-xXF
5mm is ample enough
https://www.ebay.co.uk/itm/STOVE-RO...hash=item3d4352cbb4:m:mp-aK_SaUGTdOyTNl1qfvHw
is all we use with rocket stoves