An alternative to the Howgarts Express

[McColm]

The London Midland and Scottish Railways liveries are similar in colour to those chosen by JK Rowling in her Harry Potter series of books and films.
I must admit that the streamlined coronation class in 00 gauge would work very well as the Hogwarts House express train.
The scarlet and gold would be Gryfindor.
Blue and silver is close to the blue and bronze colours of Ravenclaw.
Black could be used for the Slytherin house although a in some areas the green and silver does look blackish.
Then there's Hufflepuff in yellow and black.
You'll probably need to get a body and paint it.
An alternative is the Dapol static plastic 00 gauge C085 Battle of Britain class locomotives moulded in grey with minimal details. This would make an interesting project as well.