Getting a house before or after your engaged?

So my boyfriend and I are really serious. We both have stable jobs now and we know we want to get married we are just trying to figure out when, but we are thinking in the next year and a half. My boyfriend keeps asking me to help him make a floor plan for a house, and to talk about how many rooms and bathrooms and stuff we would want. I would love to do this, but is this something your suppose to do after getting engaged and figuring out when we are getting married and everything so we know when we would be moving into said house? We are pretty traditional and I don’t want to move in with him unless we are married. He doesn’t either and he knows that so I am a little confused?