OH god yes it is,1st two i did was bloody hard work off a roof ladder with lance plus the weight of the hose and with 3000psi firing out its hard work esp if the pitch of the roof is steep.
My local hire place does this one man cherry picker so much easier but still can be a pain if you've got like close semi detatch houses,dormers,long valleys to get to,dont half save coming up and down ladders all the time just to move a few feet over.
I dont want to put you off,but as my last post said get all your legal crap up to scratch,just do your homework 1st.
I've a photo of a converted stables i did about 3 years back,wasn't to back off a roof ladder cos the pitch was not as steep,still took ages though,as the tiles were like biscuts,i'll try and dig it out