Start building a queen-sized slat bed by routing a 1-inch wide by ½-inch deep groove along the length of both the side rails. These grooves are where you will fit the vertical slats. Rout ½-inch wide by 1-inch deep grooves into the front of the 1 ½-inch x 3-inch rails. These grooves will be for the top rails at the head and foot of the bed. Drill three ¾-inch diameter holes that are 1 3/4 inches deep at the ends of the rails that will be the head and foot boards.
Drill two more holes for dowels ¾ inch from the vertical posts' side as well as in the middle. The side rails need two dowels each.
Line the six 6 x 1 x 17-inch vertical slats and on the posts to determine the spacing. The vertical slats should begin 2 inches from the rails' top, and end 16 inches from the bottom. The holes in the rails for the dowels should help you. Mark and drill holes in the vertical slats.
Lay all of the slats together between the rails for the top and the bottom and measure what remains, then divide it by 7. This will be the length of the seven spacers you will cut from ½ x 1-inch wood. Slip the dowels into their holes with plenty of glue and slip in the rails. Clamp them in place. Glue the spacers in place and clamp them also. Repeat the process for the other end of the bed.
Line up the long rails that don't have the grooves with the bottom rails on either end of the bed. Drill holes for the dowels in the end of the rails, then insert the dowels and slip the rails in place. You can choose to glue the side rails or use a clamping system of your choice so you can take the bed apart easily for transportation.
Lay the 2 x 2-inch x 6 foot runners on the long rails inside and glue and screw them in place. Cut a 1 ½-inch groove in a block of wood and screw it to the end rails and underneath the slats. Place the 4 x 1 ½-inch x 7 foot rib into the groove.
Place the 12 slats on the runners and space them evenly. Screw thee slats down so they don't move, such as the ones on either end and the one in the middle. Secure the rest by running a length of nylon string on top of the runner and the slats, and stapling in between each slat, making a loop into which they'll be secured. Do the same with the other runner.
Finish the bed however you want with paint, varnish or wood finish.