im trad as well{15 yrs!} ::)i charge 20quid a side on a normal 3 bedder and takes me about an hour normally.i use 2 cloths and windowlene.come up great.i dont go lookin for this work as i have a full round so i always price on about 40quid an hour.the same for inside gutter cleans,soffits,fascias etc.itll take u longer than u think but once uv done a few ull have a better idea what to charge.when i started 15 yrs ago i did all sorts to get work and earn money,im not bothered if they say no anymore!always use a ladderstopper if u work alone and mitts.good luck!
regards dazmond