When using SetupBuilder for packaging MSIs we almost always have the requirement of specifying the installation directory by directly specifying <Property Id="INSTALLDIR" Value="C:\PathToInstall"/>.
I propose the addition of a parameter installDir for the MSI task to set this directly in build.gradle.
Usage would then be like so:
msi {
from "bin"
include "**/*"
installDir = 'C:\PathToInstall'
}
If this proposal is accepted, I would take care of the implementation.