According to Vastu Shashtra the most suitable place of mandir is North East corner. It is also called Ishan Kone. In your home/flat North East comes in balcony. So you can sit there at pooja place. It is beneficial. You should plant a Tulsi plant at North East corner. The pooja sinhashan and picture of God Goddess keep there. Pooja sinhashan is also fix at North East corner in balcony is also. Sinhasan should be facing west.
,I bought west facing entrance flat in which builder has not given any provision for puja room. In my flat north east area is balcony and living room. my balcony is very big and I cam construct puja room into it please advise is it ok),