Resizable dialogs require that controls are present that the user may want to resize to better use. In general, items such as labels and buttons will not need to be modified by the user. They will be covered by auto-layout. Controls that do need to be resizable are multi-line text boxes, data grids, etc...

To set up a resizable form, set the columns and rows that should grow to a percentage style. The TLP  and the form should not be set to autosize. This will get us into problems with being able to resize larger without being able to resize the dialog smaller again. Default padding and margins around the borders will suffice. The TLP should be anchored top, bottom, left, right.

The controls that need to grow will need to be anchored top, bottom, left, right. The other controls should be anchored however you want them to look on the form.

Here are two screenshots of a resizable form before and after resizing.