It does sound like a great idea for a map. I'd highly recommend doing that.

The reason for the specification of 5' squares is that many games (not just D&D) run tactical maps at this scale. It's possibly the largest segment of maps created every year, and a useful scale for lots of people. If you have an interest in producing maps for games that's a good place to start.

I don't think we've ever disqualified a good map, so I would go with your original idea and see about providing a detail with a small 5' tactical grid over it.