I agree with the others- asking for a tour never hurts. The worst they can say is "no."
I can offer a couple things...
- It depends on where the story takes place. There tends to be a certain common style to public facilities i.e. you'll find a lot of FDNY fire stations are little brick things with only one or two vehicles, as opposed to the west where they will have larger central stations with more vehicles and EMS.
-If you are thinking a newer building, then it is possible it houses ALL of Public Safety. I worked in a station that had fire and EMS on one side and police on the other (and never the twains shall meet... good times!). The entire place was locked with swipe cards and neither side had access to the other.
-post 9/11 brought A LOT of security changes. Even in the older places they have created secure areas that restrict access to all but the lobby.
-Like SL mentioned, some places don't have any secure prisoner areas. If they do, there is always some sort of sally port to drive in to unload people and process them. In my area there are very few municipalities with their own police force. Many contract with the county sheriff, so there are only sub-stations which are essentially offices. If you get arrested you go to the one jail- in some cases 50 miles away. Accessing the police means going to a sub, calling the dispatcher, and waiting for someone to meet you there.
I can give you a lot more on fire/ems if you need it, but I also have a co-worker who is an architect. His firm does A LOT of public safety buildings. I am sure he can provide a floorplans if that would help. PM me! (and good luck!)