Can't get SITL to build successfully in the px4-sitl Docker Container

I followed the instructions for running the SITL inside a docker container. it was setup successfully, but when i run the ’ build px4_sitl_default gazebo ’ command, it gives me a Cmake error as follows:

CMake Error: The current CMakeCache.txt directory /src/firmware/build/px4_sitl_default/CMakeCache.txt is different than the directory /home/harshil/Firmware/build/px4_sitl_default where CMakeCache.txt was created. This may result in binaries being created in the wrong place. If you are not sure, reedit the CMakeCache.txt
[0/1] Re-running CMake...
CMake Error: The source directory "/home/harshil/Firmware" does not exist.
Specify --help for usage, or press the help button on the CMake GUI.
/usr/bin/cmake -H/home/harshil/Firmware -B/home/harshil/Firmware/build/px4_sitl_default
ninja: error: rebuilding '': subcommand failed
Makefile:217: recipe for target 'px4_sitl_default' failed
make: *** [px4_sitl_default] Error 1

I am running Ubuntu 18.04 with ROS Melodic

Okay so i got it.
you just have to delete the build folder. cause it build everything from scratch.