Are there any examples of a cascode device in the PDK? I'm looking at using a multi-finger 35/0.15 nfet in common gate cascode as the first stage in an amplifier targeting 10 GHz. The textbook layout (i.e. Razavi RFIC page 281) just shows two adjacent gates with no inter-device contacts, which looks ideal for RF performance. On the other hand, this Magic treats it as two separate devices. If I use the former method, would I have to manually tweak the model to set the inter-device source and drain to zero (periphery and area), or is Magic going to extract this properly as drawn?

There are no cascoded gate structures in the PDK, but yes, you can just draw the transistor structure manually. It will extract correctly. The inter-device source and drain will not be zero; it will be whatever is the area and perimeter of the diffusion between the gates. But it should be minimum. A cascode checkbox option for the MOSFET device generator would be a nice addition.