I’m not sure I fully understand your request.
Did you see this video on how to get started with the PageBuilder? It shows how to make a three columns layout (building one column with a width of 4/12 and afterwards duplicating it).
Or, you can add three columns, set each width to 4/12, and then add your elements inside the columns (image/text/sidebar).
Or, for more complex layouts, you can use the custom container. Take a look at the example 4 from this page to get an idea about how you can combine the columns inside this element.
In case you don’t succeed, please give me a link to your page and tell me how you would like it to be.