You say 'they been charged £100k' I assume you mean quoted £100k. Looks about right but could possibly be reduced a little.
£30k to erect and £15k to dismantle = 45% labour ratio. Do you feel that you can provide all the materials and transport both ways for around £27.5k, leaving £27.5k for your o/h, design and profit. Have you agreed their occupation period and a rate for additional hire thereafter? This is essential to hedge your costs.
In reality only you will know how your teams work and if there is profit for you.
"i only put the scaffold up. i have nowt to do with pricing. its probably 3/4 the way to completion. i was only wondering about the labour % !!!! "
So long as your money is paid at the end of the week dont worry about percentages - Thats the govenors problem as he will be funding everything until (if) he gets paid the contract value.
What type of roof is it g-scaff?