Don't be afraid to change the number of cities. Maybe it is really the same city told of by six different sources at six different times in history.
I have a couple cities for the living where my PC hang out, and dozens that are known by name whre they never go. You have a little different problem it sounds like.
Well, if you don't trust yourself to make one up from whole cloth, try one of the back issues of Dragon mag where they had actual old maps (redrawn for more-modern use and readability, I think) of old European cities: London, Prague and I think Paris were done. Someone on the WOTC boards should know what issues.
I'd be inclined to redraw the city on large paper, like 18x24 artist paper, and then start plopping down the key adventure points you have in mind. Flesh out some of the un-named parts where you think the PC's might end up and then just rely on the main bits of the map. Remember, all maps leave the little streets and alleys off the drawing. Just because you don't see a way from point A to B, doesn't mean there isn't a twisting way through the old town.
To be honest with you, I take as many of my dungeons and towns from pre printed maps in books, boxed sets and online as I make up for myself. It's just easier. And some of the maps are pretty. Go to WOTC's Map-of-the-Week page and scroll through the years of stuff. Lots of dungeons and a couple very good city maps, with more added from time to time.
If you are looking for aadvice on where to put every trap or secret door, well, My best advice is to do this:
Make sure that everyone in your game group has something (special?) to do each game night. Plan your dungeon, or city, or whatever, so that everyone gets some good playing in when they are at the table. If that means a lock to pick for the Rogue, and a slime for the wizard to burn, and maybe a detect traps requirement for the cleric, that is pretty good. Put in a few items to deal with for each night, and maybe try to have a fight or non-hostile encounter. Let the fighter try to deal with a guardian skeleton or some such.
I don't rely on random encounters. I try to plan for some reasonable encounter in the environment the PC's are in. For an Ancient city, I have old homes and stores, maybe empty and maybe guarded by a golem or restless spirits. Tombs have traps and guardians. Libraries have a cool tome that everyone needs to see and someone needs to read, sometimes many good books.
I know I'm not much help with specifics, and help-book references, so I guess I better wish you good luck now, and let someone else post.
- Turhan the Red