The flat roof here makes it easy!
But it's really prone to leaks.
The way my baro is set up I can see the flue beyond it. Some fly ash buildup I saw might have been from last season's minor wood creosote. Like the ash stuck to it. My old Sears shop vac has a pleated filter that seems to handle the ash well.
Nice and clean now, and with no ash in the fire, it's really putting out a lot of heat.
My chimney is only about 9' from the thimble to the cap, so far so good with the draft.