Explanation

• Are you Buying that house?
• کیا آپ وہ گھر خرید رہے ہیں؟
• ***
• "Buying" is a verb (used with object), bought, buy·ing.
• "Buying" is best to keep the meaning of the original sentence
• **
• The "-ing" form can function as a noun.
• These nouns are called gerunds and can be the subject of a clause, followed by a third-person singular (he/she/it) form of the verb