In article , "Capitol"
says...

There appears to be nothing to stop you from doing this. If you look at
church roofs from the late 19th century, many of these used straining
rods at high level to prevent the rafters from spreading. I'm sure that
a bit of old style O level maths would let you calculate the forces
involved and let you determine the sizes etc required.

I expect the rafters and walls were rather more substantial than those
in the OPS garage though. If he's going to follow church architecture
he should build some nice buttresses to support the roof.