I cloned Objective Resource from the yfactorial ObjectiveResource github repository, initialized the git submodules, and tried building it under the SDK for 4.2.
I ran into two problems when trying to build. First, it complained about not knowing where the SDK was. To remedy this, I went to Project -> Edit Project Settings -> Build -> Base SDK, and changed it to latest. It was originally looking for the 3.0 SDK, which wasn't installed on my machine.