Varying opinions. Wide side helps them keep their feet warm, but you are in a warm climate. Some people use about 2" dowels, some use tree branches of varying diameter. Some chickens prefer a platform or something even wider than 3.5". You didn't mention breed. You will be the best judge of whether they are comfortable on the narrow side. Bantams or Leghorns might do fine, whereas a 15 lb. rooster will probably want a shelf or ledge.
I have several breeds of large fowl. I could tell that they were happier when I changed the roosts from the 2" side to the 4" side; I guess they were more comfortable. But I have an Orp hen who insists on sleeping on the top of a nest box (yes I left the tops flat; scrounged boxes with linoleum-type stuff on them.) I just scrape her poo off in the AM. Yet a couple of other Orp hens prefer the roost.