Better option is to apply to builder to execute registered sale deed in your name and wife name 

2) you can later execute gift deed for your share of property in your wife name 

3) builder may not agree to execute registered sale deed in only wife name 

You need to execute a fresh agreement with her in this regard. 

Have you paid 3% stamp duty on ATS ? or just simple agreement a with 500rs registration fee paid ?

If 3% stamp duty on ATS than now when you will register sale deed, you can introduce your wife as joint owner or give her POA to purchase on your behalf.

OR sale deed can directly be register in your wife name, builder has no objection if you register the peropty to whomsoever.Only issue will arise in your case 6% stamp duty, in wife case 5% stamp.

So 2% stamp duty more stamp duty payable if register in wife name and this may object by sub registrar as ATS is in your name. so highest 1% more stamp duty will be paid.

An agreement to sell must have been done by the builder. Now a registered agreement should be done and a rectification deed can be done wherein your wife should be made a second party. Then you can register the sale deed.

Regards 

1. If the sale deed is already executed and registered in your name then only by changing the woenrhsip in full and or in part your wife can be added.

So in that event you can make a gift deed to make your wife full and part owner of the same land.

If you have only sale agreement registered then n the sale deed you can make your wife full owner by you becoming a confirming party to the sale deed. This is permissible and this would save your stamp duty towards the gift deed.

Yes you can do it the builder can register the flat to your wife's name and you can be confirming party in the sale deed. 

you have entered into an agreement of sale with the builder. If your agreement of sale has nomination clause/ clause with narration of sale deed may be executed in favour of third person Or any family members, the builder can execute sale deed in favour of prospective purchaser and you becoming a confirming party in the said sale deed. 

The registered sale agreement in favor of your wife has to be cancelled and a fresh registered sale deed has to be executed in your favor.

Whether it is between husband and wife or anyone, it is illegal and invalid to register the sale agreement in favor  of one person and to execute the registered sale deed in favor of another person.

Dear

Change of owner name is allowed

if builder agrees to it you should enter a triparty agreement with builder and your wife are parties to agreement and you will become the confirming party. By this way can register the flat on your wife name.