My son recently celebrated his 6th birthday and really wanted to have a construction themed party. The cake was simply decorated with construction orange icing, had a caution tape border around the top, and was finished off with grass and a crushed Oreo cookie "dirt road". I then placed a brand new front loader toy on top and filled its bucket with more crushed up cookie. I also found some awesome construction cone shaped candles at Target. He absolutely loved it and it was very inexpensive to make!
Well done! Looks great! Happy 6th birthday to your son :)