Yeh, I get that its a complication. Not sure How Ray's is, cause I think its a continuous slab @halifaxhops
Could do separate slab for that area. Don't think you want all one in a 30x 40 anyway. A few smaller and less likely to have cracks later. I know in the cold storage the crane runs for setting steel and roof units were thicker slabs than the rest of the floor.
My 32 X 42 shop had 8in poured on the top level, ,and 10in in the lower level, where the lift is. Has a 4in grade front to rear, no expansion joints, no cracks in 18 years.....:thumbsup: