in a lego halo box or set
Watch YouTube simply
You either need the right pieces and try to build it. Or you can buy one from Mega Bloks.
on ebay or online
There isn't a Lego Halo video game. Mega Blocks is like Lego and has build-able Halo products.
by making the body and legs and claws like the atlantis scorpion
try youtube.com
they dont have it for lego, but theres a thing like legos and it cost from $20 to $40 dolars depending where you buy it.
Lego doesn't sell Halo products. That's Mega-Bloks thing. But their Halo theme is usually found in Toys R Us, Target, or Walmart.
You get the set that includes it.
If you want instructions for any sort of Lego creation (that isn't owned by Lego) then I'd just search it and look at the first couple of links. I know that quite a few people have made Halo Lego on Moc-Pages and on personal sites. Try the related links below. Saber-Scorpion (need to buy instructions from store) Mocpages (doesn't have instructions) YouTube (IS instructions)
You cant build any Scorpion Tanks in the Halo series. No custom able vehicles. There are many MODS , in Halo 1 and 2 . Maybe then once you learn how to MOD and Hack then you can build your own Tank.