Does raising a dog for guard purposes only on the roof, with dedicated clothes and utensils for it, prevent angels from entering or is it considered forbidden?

It is permissible to keep a dog for guarding when needed. The presence of a dog on the roof of a house does not prevent angels from entering the house, as the reasons for prohibition, such as the presence of a bad odor or defiling the place, are absent. Furthermore, the Hadith (definition) states that angels do not enter "a house in which there is a dog," and the word "in" denotes ظرفية (locative adverbial). What is done by designating specific clothes and utensils for the dog is more cautious and keeps it further away from impurity. However, it is preferable to avoid dogs altogether.