Asbestos cement, it contains between 5 and 15% Asbestos, it is out of all of the types of Asbestos the safest, its called Chrysotile and consists of curly fibres which tend not to get lodged in your lungs like the blue or brown stuff (this being white). It is only of concern when it is broken or cut, it can be "wet down" but as it does not readily absorb water you need to use an "A strip" solution which then soaks into it and decreases fibre release during cutting/breaking.
The "expert removers" will charge a small fortune to remove it and will cut the metal "J" bars that hold it in place, lift it off in complete sections, wrap it in polythene and carry to their van.