Most of the information in the Yangon Street Map came from walking the streets and talking to people. There are two books, however, that we found very useful for more information about the history of buildings:
Architectural Guide Yangon, by Ben Bansal, Elliot Fox and Manuel Oka, a beautiful illustrated pocket guide (if you have big pockets) to the delights of Yangon, published in 2015 by DOM publishers, Berlin.
Relics of Rangoon, by Philip K. Heijmans, a hefty tome published in 2016 by Inya Media.

Other books we consulted include:
30 Heritage buildings of Yangon, by the Association of Myanmar Architects.
Walking the streets of Yangon, by Bob Percival, published in 2016 by projectsdada publishing.
Yangon Echoes. Inside heritage homes, by Virginia Henderson and Tim Webster published in 2015 by River Books, Bangkok.