I have been holding off adding my individual allotment plots to PO because of the number of them to add as individual polygons (and all different shapes and sizes!). I realise that creating a new geometry type might be a big deal, and it may be that this could just be a different way of generating polygons. Would it be possible to create a "Grid", where you can draw adjustable lines (in the same way as the adjustable nature of polygon borders) and where several lines meet and close a shape, this then becomes a polygon? You would need to be able to add lines to divide allotments, and remove them if two smaller plots are joined, which might be a complication too far ...