[Sachiel7]

Hoppers are definitially a good wasy to store, and possibly load balls this year.
However, have you thought of how many balls you'd acutally be able to hold having that big a hopper?
My team has found that there is more than enough room in the original robot footprint to hold a fair amount of balls.
If you built a hopper just within the original footprint (max) size, you could hold over 186 balls. Remember that there are only 80 in each match, and your robot only needs to be able to hold 10 for autonomous.
So, unless youre planning on hoarding all 80 balls, you probably don't need to extend much, if at all.

edit: a few more thoughts...
You aren't limited to not getting floor balls w/ a hopper. There are easy ways to accept both HP balls and floor balls in the same storage space.
Also, back to the idea of expanding. Note that in order to expand, your robot will need an extra mechanism to expand once the match begins. It doesn't nessicarily have to be powered, but it will mean a large (possibly) mechanism, more weight, etc.
My team has built our "small" hopper. It's not very big...I think its around 18"x24"x20", and I think it'll hold 15-20 balls. That should be plenty for us. Consider these kind of things when designing your own.