I was asked if I could buy a cake for 40 people - I called BJs and they said 1/2 sheet cakes feeds about 20 people so I would need 2 which means $50 - um, no thanks.

So, I have a 12x18 pan at home - is that a half?

I tried making one before but it came out dry.

So questions are:

Is 1/2 sheet cake enough for 40 people?
Tips for making it myself?