I was snooping round the interwebs after drawing a concept sketch, and actually found a pic that's pretty similar!
Amusingly enough, the Mia 'Rook' Sullivan character that I'm using in the Depths RP originally started as an XCOM MEC trooper.
First successful game, hired in a group of seven, picked my way through them to find I hired in two Russian brothers(not a blatant assumption), both turned assault, both kicked ass and went all the way. Even picked up a third along the way that turned Heavy.
Now while I'm a fan of the XCOM MECs, which are only somewhat larger than man sized, I'm not a fan of the classic building sized mechs from Battletech/Mechwarrior and the like. Maybe I'm just too big on tanks.
Since you didn't give any concrete numbers in regards to their specifications, I'm just going to use one of the images you provided that had some frame of reference. Assuming that little figure near the mech's right foot is a human and roughly 6' or 180cm tall, the mech in its currant stance is about 11-12 metres tall. If it was to stand upright it might be as tall as 14-15 metres. That's certainly tall enough to be called building sized.