Mark another vote for Autorealm. Campaign Cartographer is pretty good too, but just as quirky and way more expensive. I haven’t played with the add-ons, but City Designer looks like it might fit the bill.
The thing is, the type of map you want to make is almost easier to do with pencil than with CAD. The problem is with keeping the width of the streets more or less constant, like in 18th century London.
You may not want constant-width streets anyway. Most pre-industrial cities had no real standard, just “make it wide enough for traffic”, which could be a single wagon or a flood of people. If this is the case, then you could do very well with CAD. Start out by drawing simple construction lines for the streets first, then drawing rough poly-lines for the blocks. Don’t get too fussy about the boundries, these are just areas representing groups of buildings. On top of the poly-lines, start drawing rotated rectangles for buildings, keeping a side of the rectangle lined up with an edge of the poly-line. Don’t worry about getting it accurate, just eyeball it and call it good.
The really nice thing about CAD is that you can always go back and make changes without upsetting the whole map. Another great feature to learn early is the concept of layers - I’d make the street sketch lines in one layer, then the poly-lines in another, the buildings in another, the city walls in another, etc. Then you can hide the layers with construction lines, which really cleans up the map’s appearance.
Lastly, consider the final application. An RPG game doesn’t need a really great map, it just needs a really good description with a passable map. Spend more time on the area’s backstory and names and NPCs and so on, and put as little energy as possible into the map itself. People have been making do with simple sketches of maps for a long time, because it’s the telling of the story and the interaction of the players that really counts. (IMHO)
p.s. - while it doesn’t help you in this specific situation, here’s a couple of fantasy map URLs I really like:
Fantasy Mapmaking 101
The Fictional Road Maps of Adrian Leskiw