Sir,
As per rule 2A (i) of Service Tax (Determination of Value) Rules, 2006, "value of service portion in the execution of a works contract shall be equivalent to the gross amount charged for the works contract less the value of property in goods transferred in the execution of the said works contract."
For the purposes of this clause,-
(a) gross amount charged for the works contract shall not include value added tax or sales tax, as the case may be, paid or payable, if any, on transfer of property in goods involved in the execution of the said works contract;
(b) value of works contract service shall include, -
(i) labour charges for execution of the works;
(ii) amount paid to a sub-contractor for labour and services;
(iii) charges for planning, designing and architect's fees;
(iv) charges for obtaining on hire or otherwise, machinery and tools used for the execution of the works contract;
(v) cost of consumables such as water, electricity, fuel used in the execution of the works contract;
(vi) cost of establishment of the contractor relatable to supply of labour and services;
(vii) other similar expenses relatable to supply of labour and services; and
(viii) profit earned by the service provider relatable to supply of labour and services;
Under clause (ii) of the said rule 2A "where the value has not been determined under clause (i), the person liable to pay tax on the service portion involved in the execution of the works contract shall determine the service tax payable in the following manner, namely:-
(A) in case of works contracts entered into for execution of original works, service tax shall be payable on forty per cent. of the total amount charged for the works contract." Here the total amount charged includes the vale of property transferred during the course of execution of the works contract.
You are paying service tax under clause (ii) of Rule 2A of Service Tax (Determination of Value) Rules, 2006. As far as your query regarding sales Tax/ Vat issue I do not have experience to comment upon the same. Please consult a sales tax/VAT practitioner