Hi Muhammad,
You'll find that most type 1's are pretty slim, and this is largely due to their chronic lack of insulin. Insulin after all is an anabolic hormone and the single most important fat building hormone. All overweight people, for example, show elevated levels of insulin.
Sorry jenrose, but fat on its own requires negligable insulin so is not responsible for gaining body fat. Protein can build fat, but to a far lesser degree than carbohydrate.
If you want to gain weight safely, Muhammad, without disrupting your blood sugars the best bet is to eat more protein.
All the best,
fergus