AP Tristana is so much fun. If you haven't tried her yet, in this particular build, I highly recommend giving it a shot.
Max your boom boom rockets flying power and explosive shot, with priority of boom boom yaay fun rockets.
Fang -> Sorc shoes -> deathfire -> rabadon -> voidstaff -> lichbane
It feels like you're playing Veigar, only instead of having a stun most people avoid, you have awesome mobility. 24 minutes in my Ultimate rocket had a 51 second cooldown, hitting for just over 1000 damage.
I found myself not needing flash, because rockets refresh on kill OR assist, so I used Ignite/Teleport like a guide suggested. Ignite is baller on her because explosive round + ignite is a silent killer. Not sure if teleport is really the answer either, I could see myself using Faster Movement speed or Clairvoyance, but I did get a gank in bot from solo top with it so IDK.
Anywho, lotta fun. Cheap champion to purchase. Give it a shot if you're bored.