If I have a design and absolutely no suitable enclosure I make one using double sided copper layer PCB material (FR4). The (accurate) pieces can be soldered together inside the enclosure. The lid will be at the bottom fixed with 2mm screws.
Me too. The strength when the pieces are soldered to each other on both sides is very good and the enclosure gives good Faraday shielding. With very little practice, the solder welds are very smooth and uniform. All you need is a good hacksaw. The solder covers for small imperfections from the cutting operation by filling in the gaps. Once the four sides are soldered to each other and to the fifth side, the edges can be easily sanded, or filed, to square and smooth them up. Standoffs secured in the corners allow the sixth side to be removable. Easier to work with than metal. Large enclosures would require ribbing pieces soldered on the inside to give good strength, but I usually go to the purchased enclosures for those. Takes paint very well, and looks nice when finished.