Hi Gabby, i take it from your grammer and inexperience of UK market rates that you are new to the UK and that your "builder" that complained was annoed because he considered you too cheap?
well thats market forces and life! the JIB who set pay rates for the trades reccomend a rate of about £450/week for crafts people, but thats as an employee. Iff your self employed you have other overheads to consider.
Rates charged will vary depending on which part of the country you live in. if you live and work in the midlands, i personally think that a daily rate of somewhere between £150-£200 is a reasonable rate.
Others will not agree with what ive said and it depends on your personal situation and how busy you are if your fully booked then put your rates up a little, if youve got no work then drop them accordingly. Its not easy to get it right to begin with but youll get there.
Try to avoid bargin hunters and people who expect "mates rates" and just provide a good service at a reasonable price.
Hope that helps and good luck with your business.
Mark