When planning a form for transference into another material and size the simplest way is to draw the three elevations to the scale required and, if possible, trace it onto the sides of the block of material being used. Even if you are building the form in the round from clay, wire or plaster it is still better to understand the elevations. Where a very complicated shape is required then even more studies from important angles will be needed for reference. If the carving is in wood and planned in this way then all you have to do is cut out each elevation at 90degrees on a bandsaw from each elevation and then round up the form and carve in details. If in polystyrene then cut out the form with a hot knife and then round with sandpaper or a surform. If in clay then you may lay the basic form on to the plans and mould each elevation to shape firstly, before adding details. Note - (clearly the basic rules of building in clay should be followed when doing this).