If you wish to author problems please think of 2 to 3 problems and bring them to the next hack night. We want to have two months of problems ready for the August meeting.
Guidelines for problems:
A reasonably competent rubyist should be able to solve the problem in an hour. Try to keep them in the 3 - 6 range of difficulty (where 0 is new to ruby and 10 is Matz). Graphics, algs, design question, whatever makes you happy. If background knowledge is required links to places to learn that stuff would be helpful.