I encountered an issue where my built was killed on the official build server (build.snapcraft.io) when using make -j on git://code.qt.io/qt/qtbase.git. I manually limited that to make -j8 and it seems to work fine now.
It would be nice if the CPU and RAM resources could be arranged such that software can be built with all available processors and without manually setting the number of processes.
Additionally, the web interface for the builds should show that the build process was killed by the oom-killer. In my particular case, this was difficult to see because the build process gave some assembler error. Only by https://stackoverflow.com/a/25584112/8144672 did I find that this was indeed an issue with the process being killed, and not with the actual build process.