The slabs are made using a vibrating table.
Also upside down, inside surface down and outside up so as the finish can be applied, the opposite to paving slabs.
You would also have to gauge the mix well with the right amount of water etc.
I knew someone who tried the paving slabs for a living and almost went broke till he got the mix right!
Is a wooden workshop a no no.
I made mine out of 22mm ply and 4x2 timber, even bought anail gun to make it all easier.

Peter