Well, I've never built Recon helmet, but I believe, looking at your picture and a reference image of a Recon's bucket, I think that you might could start with part of the sides and base. Again, having never built Recon stuff, I can't be a voice of wisdom. This might need somebody else's help.
Perhaps you could try constructing the sides first, to be sure they are the right length, then do the bottom, then the top, and lastly the front. That's just my recommendation, so you do whatever seems best to you.