I'm assuming it is a flat pan. Definitely a lot of arch build threads out there. Most of them are quite good and have good detail on the build. In the end it all depends on what you have to work with (materials or budget).
http://mapletrader.com/community/sho...2x3-Arch/page3
There is a recent thread for a 2x3 arch build. Zucker Lager also posted a pic of his 2x3 which others have used his plans for similar builds. You could message him and I'm sure he would share.
Camp Wokanda
Peoria Park District
2023 - 210 on 3/16 shurflo, sap storage shack w/ 1100 gallon tank - 123 gallons
2022 - 210 on 3/16 shurflo, homemade vac filter & water jacket canner - 104 gallons
2021 - 215 on 3/16 shurflo, added 2nd membrane to RO - 78 gallons
2020 - 210 on 3/16 shurflo, upgraded hp pump on RO - 66 gallons
2019 - 150 on 3/16 shurflo, Deer Run 125 dolly RO - 73 gallons
2018 - 120 on 3/16 shurflo, 2x6 raised flue w/hood, homemade arch w/ AUF & AOF - 34.5 gallons