Your story doesn't make any sense whatsoever.
Oxy/Acetylene equipment will cost a lot more than $200 unless you
find something used. It would not be the correct thing to use to
join sheet metal on a roof.
I doubt the previous work was done with butane and aluminum. I
suspect that it was propane and solder which is aluminum colored.
I would be VERY worried about your workman's skill and knowledge
if he told you this. A propane torch costs about $30 and could be
used to solder together sheet metal, but would not be the tool I
would use, especially on a roof with tar paper and other
flammables. Professional roofers use heavy soldering irons with
stick solder and flux.
Flat sheet metal is not normally used on a roof as it is very
difficult to hold down without putting holes in it, and is very
prone to "oil canning". Normal metal roof panels are corrugated
or formed into standing seam pans. Every effort is made to keep
fasteners hidden or water tight.
What are you trying to do? With more information perhaps someone
can help you
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