Sedum Help

At my work we have a a few roofs with Sedum. We have decided to maintain it ourselfs and i am the lucky one that gets that job.
Im just unsure on a couple of things.
1. We would like to add some (Meadow Flowers) to the Sedum to add some colour to it and to make it more nice looking. Is this possible and how would i introduce seeds to the sedum?
2. Is their a weed killer that is suitable for sedum or is the only weed killer my hand?
3. What is the best tool for maintaining the sedum roof (Lawmower / Strimmer)
4. Has anyone got any tips on maintaining a sedum roof.

Thanks and sorry if this is in the wrong section.
Chris

 

A picture would be nice.

 

Im back at work tonight, ill take a few pictures then

 

Sorry the pictures are bad. Had no access to roof so these are from CCTV. The sedum is in a shocking state and need attended ASAP