Very easy with paths.
First you create two guides that are centered in the picture, and you set View ➤ Snap to canvas edges (View ➤ Snap to guides is also necessary but should already set).
Then you create three paths. For each path, you create a rough shape, and then you drag the anchors to where they should be (and the snapping you have set previously will make this very easy).
You then stroke the paths. The paths are stroked with the foreground color and in the Line mode you can pick a continuous or dashed line.
Note that when stroking the square, since the path defines the center of the line and
since this center is on the edge of the image, half the line won't be rendered, so you have to specify aline width that is the double of what you want.
First you create two guides that are centered in the picture, and you set View ➤ Snap to canvas edges (View ➤ Snap to guides is also necessary but should already set).
Then you create three paths. For each path, you create a rough shape, and then you drag the anchors to where they should be (and the snapping you have set previously will make this very easy).
You then stroke the paths. The paths are stroked with the foreground color and in the Line mode you can pick a continuous or dashed line.
Note that when stroking the square, since the path defines the center of the line and
since this center is on the edge of the image, half the line won't be rendered, so you have to specify aline width that is the double of what you want.