Hi titus, that's my nephew's name by the way

i am not a monitor but iguana owner. However I researched your topic since it was sorta left open and it looks like you need a hide box that will fit your size monitor and let him/her comfortably turn around in. My ig is about 9" snout to vent length and I use a large shoe box upside down with a hole cut into it. The box is about 10" by 12" and goes about 6" tall.
The important note is that the said hide box should increase in size to accomodate your pet. I don't believe there is a standard to the size as long as it gives the reptile what I call breathing room.
I hope this helps
-brandon