Works contract tax

Im a civil contractor from vapi (gujarat). I would like to know more about works contract tax and how it is applicable in my field. We buy construction chemicals from local source and use same in different projects for numerous clients across India. 

Here we are buying the material but not selling it directly to the client but instead using the same in building their structures.

Awaiting comments from experts.

Regards

Karan Seth

09974733311