Please give suggestion on buying a shared property

The question is about the additional floor to be constructed and not about the floor you plan to purchase now.

Actually, the land underneath shall be equally shared by both the owners, i.e., the ground floor and first floor owner equally.

Therefore a new person constructing a house above the first floor cannot claim a share in the ground beneath. In the given situation the floor above the first floor i.e., the terrace rights are jointly owned by both the first and ground floor owners.

IN THAT SITUATION, BOTH THE OWNERS HAVE TO CONTRIBUTE FOR CONSTRUCTION AND DIVIDE THE ADDITIONAL FLOOR BETWEEN THEMSELVES AS PER THEIR MUTUALLY AGREED CONDITIONS AND CAN GET THIS AGREEMENT REGISTERED  TO AVOID ANY DISPUTE IN FUTURE.

Your concern about your male siblings may dispute or even deny your rights in the later stage in the event they construct the additional floor on their money or your father's money, hence you may first enter into an agreement in this regard and get it registered to protect your interests in the property.

Sir , Whatever you said is 100% correct regarding share of land beneath the construction.

 But , i would like to mention that , in the 160 sq yards , at present only 1 bhk is there in both below and upper portions , also these are old kind of construction, with lesser amenities , The value is only for the land , also it is in society and very near to the main road . 

So family plan is to , just demolish whole old construction and construct a Whole new one . 

As my family promised to have a agreement to allot a floor for me.

 As you said i shall have an agreement to avoid disputes later on , pls do mention what sort of agreement i shall have ? 

or else would you suggest me to give equal share of amount for construction of new construction ? is it a good idea ?

If not , if my famiy constructs whole new building with my father/brother's money(i e loan)  ,  will i not have right to claim for the portion as they promised in agreement ? 

(note: we live near by parents house , we had plan to buy a land or a flat, rather to buy somewhere, and as my father owns lower portion, i have took a step forward to buy the upper portion . )

Sir kindly pls let me know , if one person owns the land i.e registered on his / her name  i.e my father / myself  and , if my brother constructs in it with his money(loan), what rights will he have ? 

You are asking too many questions instead of arriving at decision or understanding the situation and take a wise decision.

If you are not able to take a concrete decision then you should consult an experienced lawyer in person with all relevant papers or at least a  phone consultation with the details so that you will be guided with appropriate steps to be taken in this regard at right time.

As you own the upper floor, you are also entitled to a share in the land underneath the building hence you have equal share in the land at par with the owner of the ground floor 

To have a clarity and avoid disputes in future sir, Thanks for your response sir.

You are welcome for your appreciations.