My son is your typical digger/truck/tractor mad kid and for his second birthday I decided to get creative and make him a cake reflecting that.
I had a good look at all the cakes on this website and then ended up getting the idea from one of his t-shirts which had a 2-D picture of a dozer on it. Armed with a little more confidence from looking at this website I decided to brave making it in 3-D.
I cheated a little and got my Mum to make me three sponges (as I can't bake a sponge to save myself) and I then cut out the shapes in needed referring to my "pattern" on the t-shirt. I used a sponge due to it being a lightweight cake.
There were essentially five shapes. one was the base of the dozer and then another front square on top of it (I used jam to 'glue' these together). The next two were the tracks and then the 5th one was the blade at the front. After re-doing the blade shape I had approx half a sponge left over. I guess it depends how big you want the cake to be as to how many sponges you need.
Once I was happy with the shape of the cake I got the buttercream icing out and coloured it the yellow and black I needed. Bear in mind that I used liquid food colouring and the black turned out a bit grey due to the colour not mixing well with the butter. I guess you could use powdered colouring, but having not tried it myself so I can't guarantee if you would get true black.
Once the cake was iced, I decorated with Pebbles (the kiwi version of M&M's), those little silver cake decorating balls, Marshmallows and Licorice strips for "tracks". The "dirt" in front of the dozer blade is milk chocolate drops. I put Chocolate finger biscuits on the side as the rams for the dozer blade, and used chopsticks to support the canopy of the cab, which was a thin slab of Lindt chocolate.
I placed a candle in the marshmallow chimney stack and the cake was finished. Needless to say Connor was very impressed with his cake, and I knew I hadn't done a bad job when he proclaimed "Digger!" without any prompting from Mum or Dad.