While choosing the placement of a Pooja Room/shelf, the following points may be kept in mind:
It is best to have the pooja room/shelf in the SouthEast portion of the house. The other alternative will be the NorthWest portion. It will be easy and better to have it installed within the western wall (as shown in the image) of the SouthEast kitchen, if only vegetarian food is cooked in the house, so that the images of Gods to be worshipped will face East and further, there will be no issue of anybody walking above the pooja shelf.
Pooja room should not come in the north east/ south west portion of a house, as fire has to be lit in a pooja room and lighting of Fire should happen only in SouthEast/NorthWest. It is not good for male members of the family, if fire is lit in NE/SW. In this situation, when a male member goes out of the house (for whatever reason including silly fights/employment, etc), it has to be understood that god has helped the entire family(including the male member) by sending him out of the house. It has a bearing on the income of the household also.
Pooja Room should not be placed under a staircase.
Toilet/bathroom should not be built above the pooja room.