I agree, it depends on the design you're going with. If you're going along the lines of something that is more like a Mechwarrior type of design, then you'd probably be best off in kitbashing various parts or repurposing a pre-existing Exo suit. However, if you're doing something that seems less like that, then scratchbuilding may be an option. I know of a member of the RPF who made sort of a "WWII Sci-Fi Nazi Experimental Mech Suit" to go with his 1/6 scale WWII figures. He did a combination of scratchbuilding and kitbashing certain parts to form the overall suit. He used a couple of motorcycle pieces, some PVC, some tubing. The design he went with was meant to look like something that was possible within that timeframe. The post can be found here
. In fact, he did it along the same lines as a short film he did called 1945A
, an alternate reality where the Nazis actually begin to win WWII through the advancement of technology (it's a very well done short).