It is quite simple, all intermediate files are placed in the out folder, which is created at creation. Just copy the out folder to another location to save all the intermediate files.
I do this quite often when I have to build different goals (for example, a product and sdk assembly that will clear each other's intermediate files). For example, just by copying out to out-sdk , and then I can copy it when I have to do another sdk build later. It saves a lot of time.