Strange to use selenite for protection, but I know that it has been mentioned in the Crystal Bible, lol. You would need to use raw wands, not polished and face the points inwards to bring in high angelic energy and face them outwards to send negative vibrations away. To portect your house I find from experience that it is far more effective to use clear quartz natural points, one in each corner, so at least 4 but maybe more, also black tourmaline is great, tumblestones in each turn of the angle outside the house buried in the ground.
Grids can be made using any crystal it all depends on the situation. Do you have a specific reason for wanting to grid? I mean something that you are protecting against? A reason? Or is is just cos?
You can also use tiny mirrors in the windows facing out to change the chi
