works contract

Under work contract u need not to charge vat. Only you have to charge service tax @ 4.12%

The amendment will not apply if the contract is covered under works contract service i.e. where Vat/Sales tax is payable on the contract.

The VAT would be applicable as it is works contract. You may examine the options available under local VAT laws which could be on regular scheme or compostion. 

The classification would be under the work contract - residential complex and therefore no liability as 12 units not there.  no service tax.

The activity is liable to VAT under works contract . For details of schemes like compositions pl. refer to  local VAT law . There is no service tax for such works rpvided in relation to single house .

how shall sec 194C be attracted to such transaction???

whether tds will be deducted on full amount including VAT/ ST???

Both VAT and Services tax applicable in such transaction. for composition scheme etc. refer the relevant state VAT Act and rules.....