Steampunk makes good use of brass, iron, rust and steam. Make sure to use dark woods, gold, iron... and a good rusty texture for a steampunk-like feeling. Cobwebs simulate steam rather well. Stone is advised against it, as is dirt. Use stone bricks, clay bricks, dyed hardened clay to make it look like brass, etc. It should look decadent, classic, post-aopcalyptic and modern, all at the same time.
Dunno if it helped.
