Ok under new rules apparently canoptek constructs are limited to
BS 4. (But apparently spess muhreens who are millions of years technologically inferior to necrons have have an automated bunker with a
BS of 3...

) so the monolith shouldn't be a construct but a piloted vehicle.
I've just never seen a pilot for the monolith or where one would go. I guess he could board it via the portal and climb up into a seat.
I'd always seen a monolith as a huge AI automated combat unit. Now I'm not sure.
I'm painting mine slowly and frustratingly, having to deal with issues the original owner and assembler left me. I painted the front panel and just had a thought as I painted the necron head on it. What if that's not a symbol? What if that head is the pilot? It might be that some vehicles don't require a full body pilot or have room for one, so the pilot just has his head separated and plugged into the vehicle.