Where to Find and Catch Rotom
From Pokemon Go Wiki
Rotom are found and captured in Nest and Habitat locations.
Nests
Rotom Nests are locations that consistently spawn Rotom.
Habitats
Rotom Habitats are spawn locations where Rotom is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: