One of the major selling points of making a traditional (ascii) roguelike is that development is all mechanics and programming. I understand that this isn't the current mainstream view of the genre, but its a great approach to making a game by yourself if you don't have much experience with art. Mechanics are also much harder than they appear on the surface, and art, once you're well practiced, is usually pretty straight forward in comparison to programming or game design.

I also understand that on HN games are mostly viewed as commercial opportunities, but if you're asking about basic pixel and game art concepts your art will probably not sell your game. Most roguelikes are hobbyist projects, or at least started as hobbyist projects, and the point of this talk is to foster hobbyist development. If art is a bottleneck, make a good game without art and then partner with an artist.

That said, Chris Hildenbrand's tutorials (http://www.2dgameartguru.com/) have been popular among the HN crowd. There are some good free roguelike tilesets on opengameart.org (Dawnlike is great https://opengameart.org/content/dawnlike-16x16-universal-rog...) and oryxdesignlab.com has some good cheap tilesets. This reddit thread (https://www.reddit.com/r/roguelikedev/comments/436sop/roguel...) is more comprehensive and includes both of those resources.