Hi, you can get the size of an item using:
$.getsize nWhere n is the item's index (starting from zero). Note that this interface was designed for Custom Edit mode, because in Generate mode the index of each element is not fixed and may change.
Also, the value returned is the size before applying random transformations. To get the final size, it's necessary to "store" the random transfomation in the item using
Tree Editor->Store Transform, and then read the value.
On the other hand, Forest Tools includes a powerful utility to export all item properties in XML format. You can find it
here. I hope that helps.