Here is a tutorial http://www.cakedalaska.com/Caked_Alaska/Welcoming_William.html
The Best tutorial was by the magic cupboard but I think she took it down, because I can’t find it anymore. She Used 10×10 square pans and cut them in to different widths, like 3in and 7 in, 4 in and 6 in, and 5in and 5 in. tiered them starting with the largest at the bottom and smallest at the top. using card board in between each tier (a little smaller then the cake so when carving the cake not to cut the card board. so you have bottom 7 in and 6 in, middle 5in and 5 in, top 4in and 3 in…then carve just a bit to even it out. Frost then Panel the top ans sides with fondant. This method work better then covering it…keep the square edges. I have a few diaper bag…1 is lumpy like the tutorial above but the rest are done like this one. Feel free to check them out. Hope this helps…Good Luck!