logs are usually cedar (pine will suffice) aprox. 18-20" in diameter is ideal preferabley a log that is nearly the same diameter on either end the one we had in college was lathe turned to an even circumference, it helps if you have where tennis shoes or something similar and flat bottomed, running shoes dont work at all and barefoot hurts alot, you want to try and get as much bark off as possible before you start because it will loosen up and make it more difficult. also the log should be about 10 feet long,
having said that if you are looking for a ballance game that will be more fun to start out i would consider buying a slack line setup, all you need is 50 feet of tubular webbing and 5 non locking carabiners which should cost you much less then a round saw log unless you have one one your property : P
