I primed the whole costume with a dark grey. For a more realistic "stone look" i finished it here and there with some brown and light grey colors.
Step 7: Arms
To give the arms the right shape i used a plastic grip which is normally used to prevent that gutters are blocked by leaves. The long part is the forearm the short one the upper arm. Both parts are connected with a small grip piece to each other so the arm stays mobile at the "elbow".