runes
9x MR per level blues
9x armor per level yellows
9x armor reds
3x Spellvamp quints

masteries
offense
1 point to make exhaust stronger

defense
1 in the summoner spell slot and 4 in the hp mastery
3 points in armor

utility
get the spellvamp and cooldown reduction for summoner spells.
Get all the bonus MS you can
Ignore CDR go for the hp regen.

summoner spells
exhaust
heal

role
bot lane support tank

Strategy
Stay in lane forever after the first trip back. Use hp regen and excessive defense to stay alive, build no power whatsoever unless it gives more spellvamp.

later on you act as an hp drain tank and make bypassing the front lines difficult or initiate by dropping a lantern and approaching the only fashioned way

Core items
hextech revolver
sunfire cape
ninja tabi or merc treads (in that order)

items you want later
hextech gunblade
banner of command

and maybe morellonomicon.. he'll have armor and MR...

keep in mind that thresh's early hp and hp regen are quite good

I actually would like to try this. Thresh currently has the second if not first, highest Regen rate in the :League right now at level 1.

Darius is either higher or lower than Thresh.