Using boxwood, all those shapes could be made at once, depending upon how big you want the plant in the end.If you want it higher, don't continue to trim off the top. Want the sides higher or wider, don't cut off main stems as they grow outward,upward. You'll have to put up with the topiary appearing ragged or uneven for awhile until you achieve the design you want. And don't forget to check your "sculpture" from all angles while you are trimming and snipping.

Use sharp hand shears that look and work like scissors, I use a pair with short blades. I think they're actually flower pruning shears. My limited knowledge of topiary is strictly from experience, so perhaps you should find a good book for more how-to's and do-not's. Good luck. Post your finished projects. Or beginning ones!