This question is very difficult to answer, because an enclosure for a wild animal can never be big enough. We always admire and are very happy about the loving generosity of individual turtle keepers who provide entire indoor spaces with adjacent gardens for their few animals and spare no expense and effort for the well-being of their turtles.
Radiated tortoises are very active tortoises with a great need for exercise. As a rough rule of thumb, you can assume that the mass for an indoor enclosure is at least should be 10x the carapace length in length and width. For an outdoor enclosure 20x the carapace length in length and width. For each additional animal 2x the carapace length in length and width. These specifications should be not be undercut! Of course, the enclosure sizes must always be expanded with the growth of the turtle. The enclosure size should always be chosen sufficiently large, so that the turtles can find different light and temperature zones in it.