I'm currently doing some Jeeves & Wooster builds for my British TV show hood. Highclere Castle serves as Totleigh Towers (OK, and Downton Abbey also), and because it was built long after castles were serving a defensive purpose, it has fancy spire-like decorative edging on its towers and turrets, rather than more practical crenellations. I'm not sure what form these would take in the Sim World: roof edging (aka specialized fencing), I'd suspect. Possibly deco spire-shaped sculptures for some of the larger bits? I've included a photo of a tower from Wikipedia for reference... see what solutions folks come up with.
P.S. Unfortunately, I don't have Mansion & Garden... did they even make that for Macs?

Here's the M&G + AL roof elements for base game. I'm also interested in more elaborate gothic build pieces, it's my favorite kind of architecture. So far I've only seen pieces close to this under the medieval tag.

I've seen stuff from that site uploaded elsewhere, but I've never actually visited before - thanks for the suggestion! I do have the "fairybulosa" fences . They look good from afar for this purpose, but they're not quite... ornately ugly enough? Anyhow, I appreciate the site link: I'm adding it to my Sims 2 bookmarks.