I'm not an expert but there's https://jaxformer.com, https://github.com/karpathy/nanochat and, of course, the original "Attention is all you need" paper at https://arxiv.org/abs/1706.03762.

Intuition: there are YouTube videos from 3blue1brown [1] and Welch Labs [2] on neural networks, LLMs, and related tech that are good.

Building: the videos/tutorials from Andrej Karpathy in Python [3] are considered to be very good at building and understanding the basics, from a small/toy neural network engine to transformers and tokenizers.

There was a post here a few weeks ago [4] on reasoning models using Python/PyTorch with links to an older series on non-reasoning transformers.

[1] https://www.youtube.com/playlist?list=PLZHQObOWTQDNU6R1_6700...

[2] https://www.youtube.com/@WelchLabs/videos

[3] https://karpathy.ai/zero-to-hero.html

[4] https://news.ycombinator.com/item?id=50245138