no worries Carole.....................I'm Cornish.........so I can speak your language................. :o)
if it is an extension, then get a price for the blockwork as a whole................rates are usually given per square metre......................a price should be much more use to you..................get three if you can..............this time of year plus the economic slowdown means a lot of tradesmen are scratching about a bit, looking for work...........so you should get good prices..
Good luck