You should avoid keeping your Chihuahua outside as much as possible. It is certainly possible under certain conditions, but we do not want to go into these options further here.
The Chihuahua is a pack animal and also a very affectionate and loyal four-legged friend. Keeping him isolated, for example in the garden or kennel, is not species-appropriate. The Chihuahua belongs in the house with its people. Period.
In addition, both hair variants (short and long hair) only have a little undercoat, which is why they often only tolerate rain and cold insufficiently.