Maneuvers generally begin and end at the same base altitude--what you might think of as your low track, above which there is also a high track where Figure 9 ends and Figure 10 begins. The different levels shown in the Aresti diagram are merely a graphic device to keep everything from looking like a plate of spaghetti if you tried to show the base levels all on the same line.

The tops of your vertical maneuvers don't have to be all at the same altitude, but it's nice to maintain a certain consistency. Also, some maneuvers (hammerhead, humpty) specifically allow a different entry and exit altitude, which you can use to make corrections for having drifted up or down in previous maneuvers, or to set up for a better entry to the next following maneuver. Other maneuvers, such as the loop and aerobatic turn, having the same entry and exit altitude (and bearing) is part of the scoring for the maneuver.

You can get the specific rules for each maneuver off the AMA website, "Competition Regulations 2007-2008 Scale Aerobatics." You need to download this document and study it--at least for the maneuvers you'll be flying. Unfortunately the names of the maneuvers aren't shown on the Aresti diagram, but you have the names you need in the narrative.

Another rule of thumb is that the exit altitude of the preceding maneuver and the entry altitude of the succeeding maneuver should always be the same. In other words, the line connecting two maneuvers is always straight & level.