Getting Android SDK
Once you download the SDK (ADT) put it in a convenient location, I keep it on my Mac here:
The reason for this location is that it is being backed up with all Apps and moved to another Mac when upgrading. We aware that after you download all kinds of versions this folder will grow, mine is about 13 Gb most of that are system-images -- and I don't even have all previous versions of Android downloaded. You will need every version you are building for, so for example I am currently using API 17 and 19.