How in hell do I make a modular isometric roof - looking somewhat good? I'm really not sure. Ok so I could cop out and do flat roofs but if I want a proper slanty roof I'm not sure how to make that modular.
This one is just one big roof tile that disappears when character enters a building, triangle wooden element in the front is part of a tile:
This (unfinished) one is made out of tiles:
You need a specific angle of slope or else edge won't tile. You need about 15 tiles for one direction of the roof (N-S or E-W). For both directions and transitions probably about 35 tiles, (let's say $5 each, slate patterns are time-consuming). For the simplest flat roof, you need 9 tiles.
Which one is better option depends on your game. If it's small game with limited number of buildings, and you don't mind many buildings in the same size and shape, using one big roof graphic could be cheaper/faster, if game is big and you want a lot of buildings in different sizes and shapes, separate tiles are better.
It would have to be non-modular, and serve as a giant prop on top of the house that fades out when you enter it. Though I haven't experimented with this idea.
Fonline does it, but it needs normal small tiles underneath big roof graphic.