You can save styles in template files, so that you don't have to create styles from scratch each time. To do this, set up the styles you want for doors, schedules, slabs, etc. Then use File / Save As to save the file as a .2ct file (DoubleCADTemplate). Place the template file in the "Template" folder of the DoubleCAD root directory. Then when you want to open the template, use *File / New, and select New from Template.
Note: This also applies to tool Properties; set the properties you want, such as door dimensions or wall width and height, and save them as part of the template file as well.