The platform build for the Apple II requires only two dependencies. You will need to install these and have them in your path before you try to build.

Java 8 (or higher). You can use either OpenJDK 1.8+ or Sun JDK 1.8+
Apache ant 1.9 (or higher)

You can check if you already have them this way:

java -version # should show "1.8.xxx"
ant -version # should show "1.9.x"

Build the tools

cd Platform/Apple
ant

Put scenario files in place

You will need acquire and place three scenario files into the appropriate subdirectories of Platform/Apple/virtual/ as follows:

Platform/Apple/virtual/data/world/world.xml
Platform/Apple/virtual/data/world/enemies.tsv
Platform/Apple/virtual/data/fonts/font.bin

Build a game disk

cd Platform/Apple/virtual
ant
The resulting disk image will be Platform/Apple/Virtual/game.2mg. Just boot it in an emulator or copy to a real Apple II, and have fun.

Rinse and repeat

Change any of the code files in virtual/src, or update the world.xml file using Outlaw
Go to step 4. The system uses incremental building for speedy turnaround.