There are several exercises you can develop further from making backwards half roll and stand up in basic stance with your goalkeeper. But if and when working on it, there are a few things you should pay attention to!
Common thing is that the goalkeeper can not touch the floor above the head with his/her toes while bending the legs backwards (lack of flexibility, core control).
The most common mistake is that a goalkeeper is pushing with hands while getting up in basic stance. This often represents a lack of the core strength.
Another thing you should take care of is if their knees are going inwards during the stand up phase.
After making sure these few basic details in performing backwards half roll are ok, then you can progress and develop many different exercises.
Goalkeeper in the video: Lauri Arkko