If building templates could be marked as patterns and show up as options in the building designer, it would make it a lot easier to add new patterns to the game and share them with others.
From what I’ve heard, the floor and walls use simple, repeating patterns while the roof use 9 patch patterns. So to support roof patterns in the same way you would need a UI to set up 9 patch rules and save them with the template.
If you get to the point where even 9 patch patterns are easy to add then you could consider supporting 9 patch patterns on floors and walls as well. This could be a way to improve the problem with repeating patterns on tall buildings, that @Allie and Chris (don’t know his username. Help!) talked about on stream 298.
To get away even further from repeating patterns you could make an extended version of 9 patch where each cell in the 9 patch can consist of x number of subcells. Each subcell being an alternative pattern that the game can randomly choose from instead of just repeating the same one. Depending on how far you want to take it, each subcell could also have settings for how likely they are to appear, if they can be rotated and even mirrored.
Tagging @Sweet as well, since I saw her comment on another suggestion about patterns.