http://otland.net/f81/real-tibia-svargrond-arena-gesior-13148/
this should be enough of an example to code the base, i can tell you the theory behind it without doing the code, as long as you have a theory you can create a code even with the basic programming knowledge
IF said player stands on tile
THEN getplayerlevel
IF getplayerlevel is >=50
THEN tile teleports player to (pos)
ELSE tile sends (msg)
IF character stands on (newpos)
THEN dosummoncreature (X,pos)
ELSE sends (msg)
IF getplayerpos is within (x,y,z and x,y,z cordinates)
THEN tile sends player (msg)
IF getcreatureposition is within (x,y,z cordinates)
THEN getcreaturecondition
IF getcreaturecondition is (X)
THEN tile sends player to (pos)
ELSE tile sends player (msg)
just an example of the theory behind it and what you might need for it to work, not saying this is all you need, but it's quite easy once you get started, the problem is how you want the arena, a chopped version can be made by editing xml documents, the code should work with version 2, version 3 beta is kinda..well its still in beta so i wouldnt use it, but thats just my 2 cents, goodluck, ciao~