If i were to rent or buy a shop i would have to pay business rates, how is it calculated?

do you pay a certain amount per sq ft/metre or does it come down to the business turnover figures - anyone know?

Check with your local council, they should be able to advise you.
Details from LB Tower Hamlets on link below

Note that the Council does not have much say in how much is charged. Money goes to Central Gov and is redistributed.

your best bang for your buck is renting a room from yourself - if you don't have one like that consider adding an office to your garage! the rent you pay yourself is tax deductable!

To rent a place you pay so much per square foot. If the owner re-models the space for you, the cost per sq ft will go up proportionately.
In a good location in a mid sized city, $25 psf is standard. Locally, in a not-very-good location, $10 psf.
Different commercial neighborhoods charge different prices based on the amount of foot traffic and its overall attractiveness.

i don't know but i want to find out!

business rates are set by your local authorities - and the amount is based on the size of the property. relief is available - but has to be applied for. (charity shops are usually automatically in receipt of 80% relief on the rates - and the local authority often allows them the other 20% too...)