I am Highly intrigued. I am an avid fan, and collector of Godzilla. Do you have a specific series you are taking your history from, or completely your own? (Aka: would mecagodzilla be alien made, or created by the humans using the skeleton of an earlier Godzilla) 

Secondly, am I restricted to the monsters you listed? 

(Spicifically wanting Gigan. Or to make a mecaGigan)