Two people have been charged in Perth after allegedly tricking elderly women into paying them a fee under the guise of doing roof repairs.

Two men visited the Mt Hawthorne home of an 88-year-old woman on Wednesday and convinced her that her roof needed repairing, before taking her to a bank to withdraw money for the job, police said.

But the men did not do any repairs and one of them stole a ladder from her home.

A 31-year-old man has been charged with stealing and trespass, and is due to appear in Perth Magistrates Court on January 22.

In another incident on Thursday, two men allegedly went to the Karrinyup home of a 91-year-old woman without permission and climbed onto her roof before telling her the roof needed repairs for a hole.

One of the men took the woman to a bank to withdraw money, police said.

A 17-year-old boy has been charged with trespass.

Consumer Protection issued a warning about the scam earlier this week, with Commissioner Anne Driscoll saying homeowners should never deal with door-to-door traders.