I have LLMs write and review design docs. Usually I prompt to describe the doc, the structure, what tradeoffs are especially important, etc. Then an LLM writes the doc. I spot check it. A separate LLM reviews it according to my criteria. Once everything has been covered in first draft form I review it manually, and then the cycle continues a few times. A lot of this can be done in a few minutes. The manual review is the slowest part.