Purchasing decision for coffee roaster

I am looking at purchasing a coffee roaster in the region of 30kg per batch.

Justwonderingif anyone has experience/advice in what to buy. I know I need a slow speed drum.

Choices are:

Direct vs indirect heat (radiation v convection heating?) drum roasters

Cast iron, mild steel or stainless steel drum?

Perforated or solid walled drum?

I have heard it said that convection roasting is the best yet some people (Amano for instance) use a direct heated ball roaster. On the subject of Ball roasters, how does the Barth Sirocco work? Is it convection? Is the ball roaster that Amano use optimal?

any help appreciated

Karl