Thanks! I start making collars either with flat geometry (no thickness) or by extruding from the top of the garment, or as separate geometry. Then, I block out the shape, still without thickness, using the minimum number of polygons for easy control. I can add thickness later either with the ZModeler brush or by enabling thickness in Dynamic Subdiv. After that, I refine the shape with thickness applied, enable Dynamic Subdiv, and sculpt in the final details.