My 85 and two 55 gallon drums have both Weber lids and barrel lids with eight 1/2" exhaust vents. My 15 gallon Mini has four 1/2" exhaust vents and Smokey Joe lid and the 30 gallon has an 18" Weber lid because it came w/o a lid.
I have experimented with a flat top lid with a Weber daisy wheel exhaust vent (4 hole) and it also worked fine, as with using a Weber lid I found meats cooked directly beneath the vent cooked faster.
So I actually prefer to cook with the drum lids with the 8 vent holes.
Mine are all Big Drum Smoker Clones, and I never cook indirect with them-thats what WSM's are for! www.bigdrumsmoker.com