Here's a Tidmouth Sheds cake that I made for my 3yr old train lover. I am a total novice at fondant, but wanted to give it a go! It's inspired by Thomas & Friends train shed. I made a scratch 9x13 banana chip cake for the base and one 9x13 chocolate cake for the shed (cut in half, stacked and sides trimmed, with icing between layers).
I used a dried fondant mix that I found at my local cake decorating shop (it's awesome!), but you can use premade fondant or homemade(?). I used gel colouring to tint the icings.
First cover the base cake with green and chocolate buttercreams. Stack the train shed cakes on top, making sure to reinforce with skewers and/or straws so the weight doesn't crush the base. Cut the roof for 3 peaks, if desired. Cover the shed in plain buttercream, and use green butter cream for the shed roof.
Roll fondant for tracks (I rolled it on top of a Silpat). I used a pizza cutter to cut out the shapes. Place tracks on cake. Roll fondant for shed body. I also used a fondant brick roller for extra texture. Place on cake for all 4 sides. Roll fondant for roof, place on roof. I also used extra fondant to make a banner on top of the roof for the birthday greeting.
Add circles from fondant for windows, more fondant for trim around shed doors (stick on with a little buttercream.
For the trains (I cheated). I went to the Thomas website and printed off a laser colour copy of a colouring page. Taped both the fronts and backs with packing tape (to laminate, a must so buttercream doesn't ruin paper) and cut out with scissors. Pasted onto door openings with a little icing ;-)
Added trees and rock (candy), green sprinkles, and made a white picket fence for around the base cake.