Full Tutorial w/Notes: http://www.worldofleveldesign.com/categories/csgo-tutorials/csgo-how-to-draw-top-down-layouts.php
NOTE: Following tutorial is focused on Counter-Strike defusal (DE) gametype BUT the technique and principle behind it can be applied to many other games with similar gameplay mechanics.
3 workflow techniques you can use to design hand drawn top down layouts. How to start, refine and finish top down layouts of your level.
Full CS:GO SDK Playlist here: https://www.youtube.com/playlist?list=PL_c7yiTIRI8pv2Z1yqoLyLU7k2j-bM435