When I built my pit, it was an offset. After battling hot spots and uneven temps for a couple years, I converted it to a reverse flow. Now it cooks even throughout, and I don't notice any difference in wood consumption between the 2. If you want my recommendation, get the reverse flow, and as stated above get the thickest metal you can afford.
Team: Smitty's Real Pit BBQ
Superior SS-3 - Courtesy of Gainesville Jaycees and Superior Smokers
2 Custom Built Reverse Flow Stickburners
Weber 18.5" & 22.5" WSM
Weber 26.75" OTG & 22.5" OTS
Weber Blue 2000 Stainless Performer