- `cpus` (int) - The number of cpus to use for building the VM. Defaults to 1. - `memory` (int) - The amount of memory to use for building the VM in megabytes. Defaults to 512 megabytes. - `sound` (string) - Defaults to none. The type of audio device to use for sound when building the VM. Some of the options that are available are dsound, oss, alsa, pulse, coreaudio, null. - `usb` (bool) - Specifies whether or not to enable the USB bus when building the VM. Defaults to false.