Find out what perimeters your market pens of broilers have to have(should be in your project booklet or your fair book)....what are the usual market weight ranges, appearance, etc. Then find out from your 4-H leader what feeds they usually feed and at what rate to achieve this market weight, size, appearance.
We found that, in regards to judging of market pens, being fatter is not necessarily the goal...at least for meat rabbits. I'm sure it would be the same for chickens. If it went solely on just finished weights there would be some seriously big and ill chickens there. Judges usually look for good muscling, general health, uniformity in size and weight(according to criteria) when judging a market pen.