Look at some of the official maps for some reference material.
In all honesty though, Valve make a big deal in their level design commentaries about not using huge swafts of fences to cordon a play area in a map, and yet in all the major official TF2 maps that's exactly what they've done. It's either cliffs, a big wall or those gameplay fences. The important thing to note though is areas where these fences or big plain walls are utilised, aren't major walls that are directly viewed upon by players, they are on the sides where players pay little attention or are too close to see large parts of it at once to notice how bland they are. For example the concrete wall at badwater's staging area, the wooden wall at goldrush's staging area.
If players are sufficiently distracted by enemies or busy travelling to engage enemies in the next area, they will overlook a lot of underdetail. You'll get some complaints from people who are specifically looking out for it in a lone-run-through or someone not actually playing the game in order to "clip test" or pedantically scrutinise the map. But you can use your own artistic license and choose to overlook that kind of feedback.