I always have two considerations / reservations before making lasagnas. Firstly, how big would the lasagna sheets be and hence, what would be the size of my pan? Secondly, how many layers can I afford to place on my pan?
I suggest that you explore these questions before grocery shopping so as to reduce wastage! In my scenario, I did not think through the first question and ended up with a box of huge lasagna sheets. Hence, it is always important to plan ahead!
Furthermore, I would like to say fret not if you do not have the perfect casserole dish. It is also perfectly alright to bake these in cake trays!