1. TDS wont be charged on GST component that is correct and same is available as per circular 23/2017 in Income tax. However even if he is asking you to deduct TDS there is no harm to you as you have to pay that much less amount to him.
2. As far as remaining amount is concerned you need to deduct TDS on same as consideration as per section 194IA means ""consideration for transfer of any immovable property" shall include all charges of the nature of club membership fee, car parking fee, electricity or water facility fee, maintenance fee, advance fee or any other charges of similar nature, which are incidental to transfer of the immovable property"
As far as GST is concerned he can charge same as same is not collected by RWA but builder and hence all the above amount are advance for providing service and under GST, the supplier of service has to pay GST on advance but why is he only charging 5% on remaining activities if they are segregated?
If the same was collected by builder association no GST would be charged on water charges and other such maintenance charges if it was below 7500 per month and corpus fund.
Hope you find the information helpful if you do please rate it 5 and provide your valuable feedback for my improvement.
Thank you.