diff --git a/BUILDING.txt b/BUILDING.txt
index f2dbf5319..5625afa9e 100644
--- a/BUILDING.txt
+++ b/BUILDING.txt
@@ -10,10 +10,19 @@ do this eventually.
 
 make
 
+That's it. Add ZT_AUTO_UPDATE=1 to the make command line to build an
+auto-update-enabled version that will update from ZeroTier's servers.
+This is disabled by default since such a build will automatically
+replace itself with our binary distributions.
+
 -- MacOS
 
 make
 
+The same ZT_AUTO_UPDATE=1 option as Linux supports can be used here to
+build an auto-update-enabled version. By default auto-updates are not
+enabled.
+
 If you are building ext/tap-mac you will need a different version of the
 OSX gcc compiler chain than what currently ships (clang). We've got a copy
 available here:
@@ -26,6 +35,11 @@ ext/tap-mac/tuntap/src/tap.
 Most users should not need to build tap-mac, since a binary is included
 in ext/bin.
 
+To build the UI you will need Qt version 5.0 or later. The Qt home must
+be symbolically linked into "Qt" in the parent directory of the ZeroTier
+One source tree. Then you can type "make mac-ui" and the UI should build.
+You can also load the UI in Qt Creator and build/test it that way.
+
 -- Windows
 
 Here be dragons.