Are you asking about how to make a custom text box? (sorry, i don't understand really good). But, if is this, the solution it's very simple
Just must create two Commons Events.
The first place, makes (draw) your custom text box. Example:
(It's a Xp custom box template, but is only a example
Next, create a Common Events called "Message ON" or like you wish. Inside of this event, put the command "Show picture" and pick you box and the correct coordinates (Wherever you this box), and after create other Common Event, called "Message OFF" or like you wish (xD). Inside this, put the event "delete picture" and pick to delete the custom box picture.
Well, now, to use our new box, must first previously any text put before the event "call common event" and call the event "message ON" (remember, in the text option, you must choose trasparent text in the command "show text"), and write your text dialogues, and after you finish to write, call again a commond event, but this time the "message OFF", and ready.
That is the method to make a custom text box, if you want do a better transition or something just is using of command (in especial the command "move picture")
Sorry if I can not understand, do not blame you, I'm very bad for the English and if this was not what you asked, well I'm sorry.