1. since no land sale transaction, therefore, no GST,

2. he might be asking GST for construction cost,

First you should have gone for 50-50% sharing ratio and it's development agreement not a sale deed so in your MOU initially owner should have mentioned that all paper work to complete till handing over flats to owner should have taken care by builder. Means builder has to pay all GST and other tax or permission charges.

Owner will just hand possession of land and against that builder will return flats after all legal formalities and taxes. 

All builder should take care as already owner has given 60% share due to this builder is going to earn double than owners share. So for barring GST from his pocket it's not a big deal for builder .

If you have not completed transaction yet go for first MOU. 

The developer is suppose to charge GST to the land owner after deducting the cost of land either at actual or considering 1/3 cost of government valuation of admeasuring area constructed for land owner. therefore, GST is applicable.

2)  the developer can recover the same from land owner and this depends on terms of contract between the owner and developer

You need to pay get only after registration and agreement. 

1. You have to execute a "Development Agreement" (DA) with the builder and therein it would be mentioned that you would receive so-and-so share of the constructed property without any monetary consideration. You do not require any other document for your share of the property except the DA.

2. GST is applicable only on sold component of the property. Since your share is not being sold to you, there is no question of GST on the same. You are receiving your share as compensation for allowing your property to be used by builder and his profits are from the Free-Sale Flats (extra flats).

You are already an owner, any number of flats construct shall be owned by you people only and builder will need POA to sale those flats. No GST or any sum payable. Builder is faking.

No possession letter needed, which flats will owned by you may have already in JDA and possession letter is just a formality which will on builder letter head. Pay him 1 rs. of paper cost.

you will be liable to GST in JDA as consideration from your end flew before completion certificate.

1. It is a Clear law that Supply of Construction Services by the  Developer  to  Landowner  (supplier of Development Rights) is a Supply for a consideration in the form of Transfer of Development Rights and therefore GST is payable by the Developer when he transfers possession of flats to the Landowner.

2. You you are not paying GST for purchase of flat but GST will be applicable on the service of construction provided by builder. 

When a developer enters into a development agreement with a Landowner, GST would become payable by the Landowner when the developer transfers possession or the rights in the constructed complex, building or civil structure, to the Landowner by entering into a conveyance deed or allotment letter.

Hence, when the Landowner receives a constructed property from the Developer in exchange for providing land, the Landowner would become liable for payment of GST.

the land holder is transferring the rights in property and in return is getting a share in revenue/area on sale of the property to be constructed.

In your case GST liability will arise on both events. 

1) Sale of Rights in land by Land Owner to developer.

2) Construction Service provided by developer to Land Owner.

So, you are liable to pay GST to builder.

Further as per GST Law, if an immovable property is sold before obtaining CC, then GST is leviable .