While placing End Plate connection option to provide Width and thickness are not coming. It is allowing to choose Flat bar from the designated drop down list.
Please follow below steps to activate user defined Width and Thickness for End Plate dimension
1. Go to ProSteel option / Options and under Shapes go to Flat steel selection lists and uncheck "Select flat steel format from list".
2. Now in the placed connection, when you say "Change connection", you will see both Width and thickness box appearing in the Dialog box.
So in this way you can activate selection of Width and Thickness in End Plate connection.