i presume you mean asbestos that is a fibrous material often used in roofing and insulation (not any more) it is usually grey and hard and often in corregated form. dispose of it very carefully
Asbestos can be different colours, white, brown, grey and blue. I think that blue is the most hazardous. If you suspect asbestos anywhere then you do need to get an expert out to check. It was often used in garage roofs, but as long as the asbestos is intact there is usually no problem, the problems start when it starts breaking up.
Try calling your local authority. Each one has an asbestos 'expert' who will be able to advise you. It was often used on council garage and shed roofs. In the 1960s and early 1970s it was used as insulation/lining between internal walls and airing cupboards etc.
If you are about my age (39) you may remember asbestos tiles in science lessons - I used to stand the bunsen burner on them.