Has Anyone Ever Given Their Players The Construction Rules In A Mecha Game?

[The Colonel]

I'm no great expert, but I don't recall a setting in which Mechwarriors are also Mech designers - customising and tinkering are common, but a full design and build not so much. Makes sense for the players - like their characters - to get the mechs they are issued with (or otherwise obtain) and then do the best they can with them.
Sort of like driving a fighter plane is exciting, being an aerospace design engineer has much less gamability. Of course, being a test pilot - which lies between the two - is well known to be exciting, but often for the wrong reasons. So is being issued a design that wasn't tested properly...