These are the regulations regarding granting of small business rate relief. http://www.legislation.gov.uk/uksi/2017/102/made
The premises on which you are seeking relief must be occupied for business rates purposes otherwise if it is not, you are subject to empty property rates
rules of occupation:
Based on you saying it is “going” to be used suggests future tense and that you aren’t using the premises for trading yet. You can’t claim the relief until the point you occupy.