A big mek is actually a regular Ork that has an affinity for technology.
Carries force fields and that kind of thing.
I would do the regular Stompa, and give it the weapons it has in the Apocalypse book. Otherwise you will be building things that it doesn't actually come with.
Dark Angels 1750 win/loss Record
Win - 23 (Belial helped wreck Ryan's puny Eldar)
Loss - 13 (Brice's Necrons wiped me)
Draw - 2 (The 13th hold out in alpha take and hold)