I had one player who's characters always insisted on stripping and hogtieing everyone, with a loop around the neck, and using it as a leash if the person needed to be moved. His characters, and the player, were a bit nuts. Now he sits in some mountains and hovers over a red button for the Air Force
That's so funny, I'm going to be a navigator in the same Air Force and my characters do about the same thing, but I just strip them of their weapons, spell components, etc.
Anyway if it's the only jail in town chances are it's going to have either one large cell (to keep all the drunks and beggers in overnight) or that and a smaller isolated one. The isolated one would look like a modern day prison Isolation Cell: It would be metal or morter walls with a metal door (no bars) and a small sliding window on the door to push a try of food through.
When designing it allow for a few things:
1) always list the DCs of the locks AND the location of their keys.
2) write the shifts of the guards down. If it's a really small town they might not have a night staff, so the poor sheriff will have to work overtime and will propably sleep on the floor by the front door, or in his office.
3) Figure out if anyone is bribe-able and list some costs and diplomacy checks to lower said costs (I'd figure 100gp per level of warrior, and 1000 per level of fighter is pretty good)
4) if the PC can't escape, what happens next? They might jail him, and send him to a larger city for trial, or just hang him themselves. Or they could let him go in 2 weeks or so (roll to see if he got a disease while staying, just to be mean)
another fun thing to do is out of a Robert Jordan novel:
have there be a large wooden or metal cage in the town square: All the villagers can through rocks and rotten veggies at the prisoner. At night he'll get cold enough to force fort saves vs. cold (it's in the DMG)
Have fun, and don't let them get away with walking over everyone, there's always a bigger fish.
Edit: fixed some spelling errors. I'm useless w/out word
