In this series of videos, Steve Rayner builds a Z80 Computer step by step. These are the links:
1 https://www.youtube.com/watch?v=9arsE2lfd2c Z80 Computer - Part 1 The CPU, Clock & Reset
2 https://www.youtube.com/watch?v=xp9r7p35nvk Z80 Computer - Part 2 Adding ROM
3 https://www.youtube.com/watch?v=4sKy_7JC7ow Z80 Computer - Part 3 Output
4 https://www.youtube.com/watch?v=NbbvuliirEs Z80 Computer - Part 4 I/O Address Decoding
5 https://www.youtube.com/watch?v=zacSn97RQaw Z80 Computer - Part 5 Adding RAM
6 https://www.youtube.com/watch?v=GaP4ACwatpc Z80 Computer - Part 6 The Stack & Subroutine Calls
7 https://www.youtube.com/watch?v=jwHq0QktENc Z80 Computer - Part 7 Keyboard Layout
8 https://www.youtube.com/watch?v=7LNHvfxpkPk Z80 Computer - Part 8 Testing Input
9 https://www.youtube.com/watch?v=UB3tTiRFrY4 Z80 Computer - Part 9 Fast Clock
10 https://www.youtube.com/watch?v=4tc1dn3p3zQ Z80 Computer - Part 10 Designing a Number Pad
11 https://www.youtube.com/watch?v=hFRM8MWOQsc Z80 Computer - Part 11 Operating The Keypad
12 https://www.youtube.com/watch?v=0-_bOCqeDdY Z80 Computer - Part 12 Thinking about VGA
13 https://www.youtube.com/watch?v=be98l3JiiNM Z80 Computer - Part 13 Pixel Control
14 https://www.youtube.com/watch?v=Bn7pCIV76A0 Z80 Computer - Part 14 Full Keyboard
15 https://www.youtube.com/watch?v=UrD9P5YGhgY Z80 Computer - Part 15 Testing the Keyboard
16 https://www.youtube.com/watch?v=lRO4IblK4gw Z80 Computer - Part 16 Live Coding
17 https://www.youtube.com/watch?v=aprq5OcIUdo Z80 Computer - Part 17 VGA Colours
18 https://www.youtube.com/watch?v=wBAGtPOg3VM Z80 Computer - Part 18 VGA Horizontal Characters
19 https://www.youtube.com/watch?v=7FAbLfRy_hQ Z80 Computer - Part 19 Video RAM
20 https://www.youtube.com/watch?v=jf0Fac01BA8 Z80 Computer Part 20 - VRAM Timing
21 https://www.youtube.com/watch?v=kSeRjlBWIeo Z80 Computer Part 21 - VRAM Memory Map