Lee
Adventurer
Judging by the aerial pics, and using the full-size pickup trucks parked nearby as a reference, the Beast's Castle structure on the roof is approximately 40 feet long east-west and 25 feet long north-south.
That's about the size of a small tract home, but placed up on the roof of the much larger warehouse structure.
Counting the castle "base"...yeah that looks about right. The main section is quite a bit smaller.