Gst on contractors service.

Most of the services under work contracts are taxed either 12% or 18%.If it's a work contract which the service provider is undertaking (he will be considered as supplier) for a private party (recipient) gst rate :18% gst for work contract on govt. purpose 12%.

As per the Defination of work contract u/s 2(119 ) means a contract for building, construction, fabrication, completion,erection, installation, fitting out, improvement, modification, repair, maintenance, renovation, alteration,commissioning, of ANY IMMOVABLE PROPERTY, wherein transfer of property in goods is involved in the execution of such contract.

So in GST , the work contract is treated as work contract only when it is provided in relation to immovable property

Itc allowed for work contract or not. and how to file Gst return for the same

Yes you may claim ITC