So for various reasons party have decided to plan a prison break and get an innocent person out of prison rather then actually hunt down the changling that was pretending to be her :). Which is great, this is exactly where I wanted our campaign to get them wandering around doing stuff off their own back and me reacting. 

But wondering does anyone have or know of a decent town prison map? I have a full on week this week and don't have time to create one like I normally would (we play online) 

Any help greatly appreciated :). 

What type of prison is it? A typical town jail is probably only a couple rooms with a guy at a desk, adjacent to the guardhouse, and is probably best done as a skill challenge of some sort, but a serious regional prison could be much larger and better guarded.

It is much as you describe slightly larger as a building as it consists of the main guard house and so has offices etc there. the players have already pre warned me they will be tracking guard changes, studying the layout, working out how to get someone in so I can see the planning and execution of this running at least 1 maybe 2 full sessions. 

Dragon Heist has a courthouse map, with cells, guard room, offices etc.