Can't you simply trust the installer and accept the default options ?
One of the many advantages of P3D4, is that add-ons can be installed everywhere, not necessarily inside the main sim folder. And in fact, all good and 3rd party add-ons that claim to be fully compatible with P3D4 should install outside the sim, which is what LM recommends, since it will result in an easier time in case you'll have to reinstall the sim entirely.
So, unless you have finished your space on C:, is perfectly fine to install SODE there. And if you have finished your space in C:, choose any other drive, like G:\ or G:\SODE, but not the folder of the sim.