HERE in your case you are executing works contract outside the state and you are purchasing materials locally(i.e,tamilnadu your site place ) and sending the same to the site to execute the related works .
First of all, you should be a registered dealer under local act and CST acts to carry out any sales or deemed sales outside the state .If you are registered dealer then what ever purchases you are making from other state tamilnadu are treated as CST purchases and you donot get any input tax credit for the said purchases and forthe same you are liable to pay taxes at the rates applicable to the transfer of goods invoved in the said works if you maintain proper accounting i.e.books of accounts for the said contract other wise you are liable to pay tax at the higher rate on the total value of materials incorporated subjected to standard deduction of labour portion.
HOW TO SAVE TAX IN YOUR CASE:
From your registered place you effect local purchases from local registered dealers and direct the same dealers to deliver the said materials to the work site out side the state i.e,tamilnadu and you claim input tax credit and after completeing the said works when you bill to dealer in Maharastra you raise tax as per your option (taxes may vary if you opt for composition or non composition scheme) . you should also understand that when you incorporate any goods from other states in the said works then the relating turnover is not eligible for input tax credit and accordingly the said turnovers should be deducted from the total workcontracts turnover when opt for composition scheme ( composition scheme means payment of taxes at reduced rate on the gross turnovers involving materials and labour component) ,to the cst purchase turnovers you are required to pay taxes as per the rate of taxes applicable in your local state acts after adding the transport charges if any applicable and not any profit on supply of the said goods.
Further if any clarifications do write ...
G.S.CHANDRA SHAKER
SALES TAX PRACTITIONER
9395323341/9951038001.