Hi, skinny pigs aren't really outdoor animals, they need a very narrowly controlled temperature range and easily get too cold or hot. Do you mean outside in a run during the day? Even with that you would have to be very careful he doesnt overheat or get sunburn. Skinny pigs were bred in science labs and dont really have any natural outdoor hardiness... what size cage do you have now? Please show us some photos of your piggy and your housing set up, then we can advise you better!
in terms of size of cage, as your piggy needs a character compatible friend then it would be best to prepare for that and get a cage suitable for two boars rather than getting a new cage now and having to change it again when he gets a friend. The measurement for two boars is 6ft x 2ft or a 5x2 c&c.
Skinnypigs are really particular about their environement, it even comes down to such silly things as scents, would you believe that more so than any other breed, they're more sensitive to hormones due to their chromosonal differences to the usual breeds, so if they're handled by a teenager they tend to show more discomfort, given the pheromones that're released, it's called the off-gassing effect, I'm sure you already know this, and will have taken the necessary steps to avoid this issue, but it's worth noting.