Daniel Pressland denies stealing and selling works by Alan Davie - whose paintings were shown at the Tate Gallery - after his death in 2014.
St Albans Crown Court heard he broke into the painter's Hertfordshire home several times over a year.
A total of 31 artworks were taken.
The court heard Mr Pressland regularly cleaned windows and did odd jobs at the 93-year-old artist's home in Hertford.
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After Mr Davie, from Falkirk in Scotland, died in April 2014, the court heard Mr Pressland broke in through an insecure window which he had noticed while working at the house.
He was apprehended during a robbery at the artists house in April 2015 - a year after the first painting was stolen, prosecutor Sarah Morris told the court.
Police found three artworks worth a total of £190,000 in the back of Mr Pressland's van, she added.
The jury heard the defendant told police he kept his ladders in the painter's garage and, having gone to collect them, saw the three works of art which he assumed had been "put out there for the rubbish".
"He said he had taken them away as a favour and he thought he would use them for skateboard ramps for his son," Miss Morris said.
Mr Pressland, of Outward Common in Billericay, Essex, has admitted one count of burglary, but denies two further offences of burglary, two of converting criminal property and two of transferring criminal property.
Co-defendant Gavin Challis, 42, of North Street, Nazeing, Essex, has denied possessing criminal property after two paintings by Mr Davie were found at his home.
The artist's agent said of the 31 paintings stolen from her late client's home, only nine had been recovered, including those found in Mr Pressland's van and Mr Challis's house.
The case continues.
A window cleaner accused of stealing paintings worth £500,000 from an artist's home told police he planned to use some of them as "skateboard ramps" for his son, a court heard.