Builder deviated from approved building plan

I have finalized an under construction independant house property from a builder who is also the owner of the plot with size 126 sqyds in HMDA layout in hyderabad. While verifying the documents I found that the construction has been deviated from the actual approved design plan. The approved plan shows construction with one bedroom hall and kitchen an d 3meters offset facing the road within the compound wall of the building. Whereas the builder has built a 2 BHK house in the same plan. Is it advisable to buy this property. Builder is saying occupancy certificate is not required for this building since it is less than 266sqyds and government will ask for mortgage of land only when above 266sqyds. If mortgage then only construction is checked for deviation. If we go by govt approved plan we will get only one BHK, everyone goes for this type of construction only, no need to worry and such things. He has already sold two more houses which are constructed similarly. I could not check with the owners of the other houses since they are not available. Please provide your inputs on how to proceed in this case. Thank you.