Welcome to the board.
It does depend on the pattern and how it will be used. If it's a very symmetric pattern or block placement that produces a secondary pattern, you may be able to add additional pairs of rows to both the top & bottom of the quilt. If there is no secondary pattern, just add more blocks. Bed quilts often have uneven borders, narrower on the sides & wider on the top & bottom (or vice versa!). Or, if its a be quilt and you are going to have a pillow tuck, you can a different treatment on the top.
If you tell us what pattern you are considering we can provide more specific suggestions.