we are having a house built and i am unsure what the band will be,
i dont know if they will base it on the house prices from 1991 in the post code area,or they will go on the purchase price in 2006?
anyone know

At the moment, council tax bands are still based on 1991 valuations. It can be tricky to predict what the band will be, because once the property is built, it will have to be valued by the local Valuation Office, who band all properties for council tax purposes. This is not part of the local council, by the way. So you can make a guesstimate, but the Valuation Office will make the decision re: banding. Be prepared for a long wait for this to happen once the property is built, they are not always very quick - so make sure to save your guesstimate of the ctax, cos your backdated bill may be quite high. Good luck with getting the post office to recognise the new property on their database as well - fun and games when dealing with financial institutions, etc, who go by what is on the Royal Mail's database. Be prepared to be told that your house doesn't exist!

See http://www.libdems.f9.co.uk/public/ctax/levels.htm for Council Tax bands and the values in Sheffield.

I bought a new house from a builder in 1999. I found that the price we paid was the price they used to do the valuation for the council banding.