I want to make a large circular pot out of sheet metal that can hold water. How should I construct it so that it has a circular bottom and ensure it is leak-proof.
Boiling water will be poured into this pot.
Soldering is the usual method, but without metal-forming equipment I'd guess you don't have, that's not going to be a likely (or affordable) road to success for someone with no experience, for any value of large.
Buy a galvanised washtub or trashcan is the direct, simple route to a watertight circular metal "pot" over a wide range of sizes. Move into "stock watering tanks" for a larger size, though most of those are more oval. Without exhaustive shopping around:
17 gallons, $30:
31 gallons, $19, with lid:
This one is 477 gallons, circular, and costs $219.
Now I've gone and started to think that would make a nice country-style hot tub, and the price is so right...
You can weld it but DO NOT breathe in the poisonous vapors produced when welding galvanized steel.
I would think that soldering would make a good seal provided you could keep the 2 surfaces tight to one another. Perhaps pop rivet the sides and the bottom together at 2" intervals, and let the solder flow. Yes DO be careful of any fumes may arise, but the galvanized metal may not get that hot enough to fume to get the solder to flow. Still, something to be watchful of...
Back in the day they used to solder galvanized downspouts and gutters together. I seen this from all the houses I worked on over the years.