So my best friends mother just called asking if I could do the bridal shower cake for my friend. I am thinking of doing a sheet cake because mom bought this as cake topper. LOL

http://www.fisher-price.com/fp.aspx?st=2053&e=product&pid=47169

So my question is what size sheet cake should I make for 50 people? And any suggestions to get good corners on the cake?

A 12x18 single layer, when cut in the standard 2x2x2" piece, will give you 50-54 pieces.

If you think they might cut them bigger, you could do a 2-layer 11x15, which when cut in the standard 1x2x4", will give you about 70 servings (so if they cut them a little bigger, you'll be sure to have plenty).