The light heavies & the heavies are around 5'7"-ish if that helps give you a general frame of reference. I'd suggest check out local / regional shows that are in your area - you can usually find photos of past shows - the dimensions of the guys in those weight classes should give you an idea of what you would expect at a smaller / not-national show. Then check where you should be for national shows (check out any of the major show photos on graphicmuscle.com - e.g. 2006 Jr. Nationals, Jr USA, USAs, Nationals are good top quality national level shows). That then gives you an idea of what top-level competitors look like.
But also keep in mind that a lot of these guys have at least a few shows & lots of years of training under their belts. Don't get hung up on getting bigger juiced more, etc. Pay attention to symmetry, fullness of muscle bellies, quality of development and balance across the board. It will take you some time to develop that thickness (like the really deep christmas tress you see in guys' lower backs on a rear double bi pose) but that just comes w/ time, consistency & persistence.
Also if you are so inclined, do a show as a novice if you want to try it.
Not knowing your stats now - you'd want to come in at the top end of the weight class for whichever you can do --- probably start in the light heavies - I think it tops at 198 lb. Guys really should be able to see striations in their quads and not have their legs look like the quad is sitting on top of smooth skin - that gives you an idea of how lean you need to be - but 196-198 lb, 5-6% at least.
If you want to see a top quality veteran national level guy, check out Quadsweep! 5'7", I believe planning to do heavy wt class at the Jr USAs in April - he's already 3.6% -- he's outrageous!