Ok well first of all you need to consider the temperature outside, if your bunny has been kept indorrs since he was born then you need to let him stay outside during the day and then bring him in at night untill he becomes used to the temperature, of course this depends on where u live, if it is mid summer and warm where you live and the night time temperature doesn't drop too much he shoudl be fine. His coat will adapt to the weather but obviously this takes time.
Make sure your pet has plenty of bedding available to use should he get cold and plenty of fresh water. Also try to ensure that your pets hutch isnt in direct sunlight as it can overheat.