I could do this as for 2 tier or for single tier but would need you to provide the Lego bit for the topper. I can add characters for each or you could provide them. I would put the cake on a larger board and have Happy Birthday etc written on the board.
I love the pink colour on this one and all the detail around the side. for single tier including all the flowers, edging around cake, pool and diving board. If you could provide the characters, or I can make the characters out of sugarpaste for each.