I have a friend who wants a cake in the shape of a square/cube gift box to feed 50. I'm not sure how big I should make it Would an 8x8x8 be too big?... Any suggestions?

She want's it to be impressive and does not mind paying for it.

A 2-layer 8" cake serves 32 and is 4" tall. So an 8" tall cake would be four 2-layer cakes = 64 servings. this is assuming a 1x2x4 piece of cake, so she'll have some leeway to cut them bigger, if she wants.

An 8x8x8 is basically two 8x8x4 cakes stacked on top of each other. An 8x8x4 gives 32 1x2x4 servings, so an 8x8x8 would give 64.

The next size down, a 7x7x7 would give 48 servings, but they'd only be 1x2x3.5.

HTH!

Well, if you're serious about the cube, then yes, a 8" cube would do it. You'd make four 8" square cakes, 2" tall each. Stack two with filling on a cardboard, repeat. You'll need to use a support system, as you're making a tiered cake where both tiers are the same width. Stack and ice. Serves 64.

......You'll need to use a support system, as you're making a tiered cake ......

Definitely use supports. Drink straws will be fine as the 8"x4" won't be all that heavy.
So, one about 2" in from each corner is all you will need

Thanks! That is what I was thinking about doing... 2- 8x8x4 stacked to make the cube. I just wanted to make sure.

Now how do you get the corners square?...mine always turn out rounded