Write off capital gain from sale of house

Dear Sir/Madam,

We are planning to construct an Independent house on our plot in rural area (Native place) and plannig to sell of a house in Delhi to finance the construction.

My query is since the construction of house will start next month and we will not be able to sell the house in Delhi before we start the construction. Is there any time frame within which i should sell off my property in Delhi to be eligable for writing off the capital gain agains the expenses of construction of house in Native.

Thanks & Regards,

Jithesh K.