I recently made one for my grandson's cremains. Walnut sides, ebony splines and spalted silver maple divider and lid, walnut and bronze pin hinges a la Rob Cosman, with antique English cast pedestal feet from Lee Valley. 11 3/4" Long, 9 3/4" wide and 8" tall. Not designed to fit standard columbarium niches, because it will reside with his mom. There is a 1 3/4" deep compartment under the lid for photos and memorabilia. Finish is shellac on the interior, Watco medium walnut danish oil on the sides and multiple coats of Minwax antique oil and wipe on poly on the lid. Cup magnet in the lid and steel striker in the top of the side keep the lid closed and a small eyebrow sanded into the top of the front side allow opening the compartment. A small brass plaque (not shown) was added to the interior of the lid.
For your purposes, you could adjust the size and the partition could be omitted and added later when needed.