Tradesmen being paid by taxpayers to work on a sky rail project instead allegedly spent weeks renovating the private home of a manager using trucks and excavators from the government job.

A Lendlease supervisor on the $1.6 billion Caulfield-to-Dandenong sky rail project has been charged for allegedly ordering the taxpayer-funded tradesmen to work on the renovations for three weeks at another manager's house.

The same supervisor is also accused of leading a wage fraud racket costing taxpayers up to $300,000, whereby tradies allegedly falsified timesheets to claim lucrative hours for shifts they never worked - a practice known as "ghosting" in the industry.

The 36-year-old man from Berwick has been charged with theft and obtaining financial advantage by deception and is expected to face court this week.

Three other workmen on the sky rail project have been charged over a separate illegal operation, in which they allegedly stole copper sheets and scrap metal from the construction sites to sell to scrap metal dealers.