Gatland's stars will spend the next three weeks undertaking personal training plans before flying to Poland for two separate training camps.
And Roberts, who underwent minor knee surgery last month, is ready for a summer of hard work as Wales prepare to take on some of the game's most physical sides.
"This is the start of our World Cup, our real preparations start now," said 24-year-old Roberts.
"The knee's good, it was getting to the point where I was hobbling around after a game, so I had minor surgery three weeks ago. I should be back to full fitness in a couple of weeks.
"I'm ready to work hard and push myself to limits I've never reached before. Every training session that first game against South Africa will be in the back of my mind."
Wales make the initial trip to Poland on July 2 and return two weeks later before warm-up matches against England twice and Argentina.
Gatland will then reduce his squad to 30 ahead of the global tournament in September.
The Kiwi has already warned his players they will go through pain and agony in Eastern Europe where they be exposed to temperatures as low as minus 110 degrees Celsius in cryotherapy sessions to aid muscle recovery.
But the 2009 Lions man of the series is confident Wales will reap the benefits before they take on the Springboks, Fiji, Samoa and Namibia at the World Cup.
Roberts said: "There will be a big emphasis on fitness and I'm really looking forward to Poland, it will give us an opportunity to reach our peak physical condition.
"We've done it before and it was really beneficial, it's also a good laugh and will be good for team bonding.
"It's the ultimate to represent your country at the World cup but it's important that we go there in good shape."