Ha ha no plating is just the posh word for MOT on a lorry. They just check more things and it has to be done at a special place rather than the local garage. My OH is a mechanic - and ours is off for plating on Monday!
I guess you might want to pay someone to check it over before putting it in and costs will add up if it needs work doing to it (we have none of that as OH does it all himself).
If its a 3.5t box it just has a normal MOT at normal MOT cost and normal garage.