Glad to help where we can, buy its kind of hard to answer non-specific questions via a bulletin board like this. Have you looked at the wiki on this site for helicopters, last years thread when it was div C, and this years thread? There are a lot of suggestions/discussions there. Another resource, the North Carolina SO organization put out some good videos on how to get started with a very simple design. You can find them on their SO site and by searching around youtube.
Now, to your specific question, the flat wooden disk. Its just that, the rules say the highest point of the copter has to be a flat wooden disk the size of a dime. Any thickness, so keep it thin to reduce weight, 1/32 thick wood will do. The rule came about because in the past some team put wooden pokers or sticks on the top that some people thought would drill into the ceiling and hold the copter up longer, but not by aerodynamic forces. This rule was to prevent that.