Home DIY

I have. There are lots of videos on youtube floating around of joiners making these kind of things, all sorts of ways of doing it, the most basic would be screwing the panels together from the bottom and top faces which will be hidden anyway. I'll list a few things that come to mind based on my experiences in no particular order.

-Use wood glue for all the joints, it will be too flimsy with must mechanical fasteners

-Typically made with 18mm mdf for the carcassing, with the back being thinner. 6mm is probably fine unless you plan on kicking the back out. Try and have at least one fixed shelf in there to help it keep its shape

-Make sure you size it to account for all wonkyness and curvyness of the alcove. Also take into account that you will have to push it around a corner to get it in. You can then close the gap off with some scribed strips or something like that.

-Square is everything. Use clamping squares and measure the diagonals when glueing it up.

-Make a plinth for it all to sit on first and get it level in all directions using little packer pieces until its just right, then screw it down to the floor.

-Painting takes ages. But if you're going for mdf, Acrlyic primer undercoat will seal it. It will raise the "grain" so light sanding after to get it smooth, especially the edges, then two coats of whatever it is you like. I went for water based satin (both Johnstones and Leyland trade have been good for me). Will need at least two coats.

-Things get heavy very quickly, things can get awkward if you're on your own

As a cheaper alternative to CNC company, you could ask B&Q to cut the panel up for you? My local one is usually accurate to the mm. If you go down this route tak ea tape measure with you and check though, I've had some shitty experiences using Selco panel cutting service.