Service tax rate if separate sale and construction agreement

My builder demolished an Individual house, owned by him, to construct an apartment. I own a 1090 sq ft apartment (UDS 523 Sq Ft) of the total 4, 000 Sq ft built up portion

We entered separate Sale and Construction agreement. Builder is calculating Service Tax on Total Value of the Property instead on. Is it correct?

I was under the assumption that by entering separate agreement, value of Service and Cost of Land is bifurcated, so ST should be only Construction Agreement Value. Please Clarify

Thanks
Govind