The way I read it, "slots" and "size" are dimensions of robot chassis, whereas "dTons" are ship dimensions and "spaces" are vehicular dimensions. The dimensional equivalents are given in the blue sidebar text on RH, pg 14. (IDK if the vehicular "spaces" are still compatible with the new VH26, since the new VH was built from the ground up, without trying to be compatible with it's predecessor.)
Anyway, a TL 18 Robot Brain Consciousness is rated as Computer/30. Therefore, according to RH pg 66, the chassis size needs to be minimum Size 30 for a zero slot cost. But a Size 30 chassis does not exist in the Robot Handbook. It is kind of interesting because the largest chassis size in the RH is size 8. The way I read that is a TL 18 consciousness won't fit into any single Zero Slot build chassis. The RH then goes into building at higher Tech Levels, but I won't do that because, if you got tech at TL 18, you should be able to make it usable at that level - so, what to do?
What you might be able to do is employ 4 x Size 8 chassis and combine them together, either ontop of each other or maybe side-by-side - I don't recall the RH saying you cannot combine multiple chassis in this way. That would give you a Size (8 x 4 = 32) and (128 x 4 = 512) Base slots. It will be the size of four Rhinos and cost 4 x Cr8,000 = Cr32,000 for the chassis alone.
I shall have to re-read the Robot Handbook, to see if that is still considered a legitimate build.