I had mine made at
Autopista Duarte, km 20
Good welding, good price!
For various reasons I recommend two or three smaller communicating tanks instead of one big one.
My own design had slanted bottoms with 3" drain valves at their joint, outside (transparent hose type) level reading with shut off valves, breathers, outlet filter, etc.
They are now 6 years old.
(You can see them on page 2 on my HP.)