Is there any drawback in buying a house facing south or south west from vastu view point?

No.........I see nothing but good......mine is that way.......but we have a covered patio on the east side of the house for morning coffee and hot summer evenings........Other than that the south exposure is nothing but good........everything that they are talking about doing in this country about solar heating and whatever is nothing but good from that prospective. Your roofs, your floors, all can capture heat....and also any special gl. Good luck!!!