>>If I went with a rack the only Lizard species I would want to keep in it would be Sceloporus occidentalis
I would not keep Sceloporous occidentalis in a rack unless it was an open-design rack with heat lamps from above. These are diurnal sight hunters - they need light. Again, the advantages of a rack are not as significant when you have to accomodate these requirements. It can be done, though.
Perhaps S occidentalis has different requirements, I don't know.
>> ...and maybe even Eumeces skiltonianus or Elgaria multicarinata...
I have probably kept both species, if not certainly their close relatives. I believe both would do well in a typical colubrid rack. But if you were already building an open design for the Sceloporus then I'd keep these in there as well.
They're all small species and don't need any significant height so finding a box won't be difficult.
>>As far as snakes go so far what I am looking at are small snakes, which have to do with my research such as Contia tenuis, Charina bottae, Thamnophis couchii.
I have no experience with Contia other than seeing preserved specimens. I'm sure they'd do fine in a typical rack provided they're not so small they can escape (aren't sharp-tailed snakes tiny??).
Charina clearly would do well in a typical rack. Many would say Thamnophis as well, but it seems many breeders of Thamnophis spp. think they do better if planted, well lit terraria.
Overall I'd say for the lizards you keep you'd be better off with small terraria kept on shelves. Have the lights/heaters sitated in a way that accessing the cages is not difficult (moveing lights, etc.).
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Current snakes:
0.2 Gonyosoma oxycephala - (Silver/Yellow)
3.3 Gonyosoma oxycephala - (Green)
2.1 Gonyosoma janseni - (Black)
3.3 Gonyosoma janseni - (Black & Tan)