What does the cryptic crossword clue "Upgrade cover on Rolls Royce, accepting European cash (6)" mean?

The wordplay uses a charade (building blocks). RER (synonym="RER") + OOF (synonym="dated slang, ‘cash’") = REROOF The answer is REROOF.

Upgrade cover on Rolls Royce, accepting European cash (6)

Guardian Cryptic #29535 | 21 Down | 2024-11-08 flower