GST ON SUPERVISION CHARGES - Goods and Services Tax - GST

Respected Members, My client is a government entity which undertakes the work of supervision of civil construction work of immovable property on behalf of other government departments/authorities/board/entities etc (herein after referred as govt.). While allocating the work to my client they mention the cost of construction and fixed percentage of supervision charges, my client then publish and issue the tender to sum other contractor, my client add its supervision charges on what ever the bill is raised by the tender allotee and issue a demand note to govt, for example: Cost of construction: 100 Cost of Interior : 50 Total Cost : 150 Supervision charges (5% of total cost) : 7.5 My question is whether the supervision charges would be liable to GST or will be exempt from GST considering the supervision charges as pure service as per the Serial No. 03 of the Notification No. 12/2017 which states Pure services (excluding works contract service or other composite supplies involving supply of any goods) provided to the Central Government, State Government or Union territory or local authority or a Governmental authority by way of any activity in relation to any function entrusted to a Panchayat under article 243G of the Constitution or in relation to any function entrusted to a Municipality under article 243W of the Constitution. on referring to the article 243W it elobrated a list in 12th Schedule serial no. 2 which mentions Planning of land- use and construction of buildings. My Question is whether Supervision Charges would be exempt from GST or it would be charges at 18% in the above case? in supply of pure service to Government if invoice should be raised under work contract as 157.5 + GST or invoice should be raised under supervision charges as 7.5 + GST Further i would like to add that 150 is the actual cost my client only adds its fixed percentage of supervision charges.