When starting out with retro computers, both fictional made homebrew or the commercial ones that were actually available for purchase in the 70s and 80s, there's one book in particular I've particularly enjoyed reading - that book is "22 micro-computer projects - to build, learn and learn" by Daniel Metzger (check out ebay or abebooks.com for a copy). Written in 1985 on the tail-end of the homebrew computer-period, it gathers what I believe is the culmination of 10 years of teaching basic electronics, digital logic and computers to people without any prior knowledge for any of those things.

The book builds upon each chapter by building a computer based on the 6802-processor from Motorola, a mysteriously similar processor to the now far more popular 6502. While it might be seen as an odd choice for a main processor these days, even the most advanced circuits are easily adapted to the 6502 as well so you'll get to play around with a piece of history and learn something while you do it.

The computer is built up of a set of modules, as a minimum you'll need the CPU-module as well as the User Interface-module that stacks on top of it. When all is built you'll have a complete 6800-compatible computer with two 7-segment displays as output and a 16-key keypad to hammer out stuff on.

A complete BOM as well as some more information can be found on the Github-page for this project. Below is a short video where I'm just displaying some program data on the computer and then run it.