Anyone built with Ytong Blocks??

I'm hoping to build a Garden Room 24sq metres with 3m wide sliding patio door. Came across this system using Ytong blocks. It sounds Quick and alot less hassle than standard cav wall build. Just wondering if anyone else has had experience building with these? Will I need a Specialist builder? Do you know any??
Thanks-Alan.

There are a few threads on this topic already including this and this. The search facility will locate others.
Leo