Top frame and cove moulding
The top frame does more than just look good: it helps protect the vulnerable end grain of the corner posts from water. Start with a length of 3 1/2”-wide lumber (this is the actual width of so-called 1” x 4” wood). Measure and mark the 45° angles for the corners, then cut them to length using a handsaw and small mitre box. If you don't have a mitre box, clamp a short length of wood at a 45° angle to the lumber to act as a guide for your saw blade. Test-fit the frame pieces together on top of the tomato cage before joining them with weatherproof glue and some galvanized finishing nails. Once the glue has dried, attach the assembled top frame to the cage with more glue and screws.
The cove moulding comes next. It's easiest to cut one 45° end first, then hold the part in position on the cage to mark the next cut. Install the first piece of moulding on the cage with glue and a few finishing nails, then repeat the process for the other three lengths of moulding.
Paint or stain before adding wire panels. In keeping with its painted Victorian inspiration, I chose an opaque oil-based stain. Apply a few coats to all wooden parts to protect them from the elements.
Cut the side panels from wire fencing using a pair of wire snips or bolt cutters. The dimensions for this tomato cage are based on using fencing with 2” x 4” openings. If you use a different size fence, make sure to adjust the size of your cage accordingly.
Once the final coat of stain is dry, attach the wire panels using U-shaped galvanized wire staples hammered in every six inches or so. Lay the cage down on its side and install temporary braces between the corner posts to make them rigid enough to resist hammer blows.