Are you going to cover the balcony and make it part of your house? Just to have it in NE, you shouldn't use area, which is outside, shared with other things, open (so may be not very clean) etc.
Is your balcony part of the room or living room?
Puja Room is a place of sanctity and should be clean and tidy both by its physical and environment.
it is also not advisable to keep the Puja Room in the Bed Rooms, where family activities take place.
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Puja Room should not be near a place where footwear/broomsticks and the like are kept, since they damage the sanctity of the Puja Room.
Puja Room can either be an independent room/shelf or even part of a shelf.
Places like the hall or the dining room are also appropriate to keep the Puja Room - subject to the above conditions.
It is preferable to have Puja Room/Shelf faces the East or North Directions. If both these directions are not feasible, the Puja Room can face the West Direction.