This is really what it comes down to, and someone saying they want to buy a "thing" vs. building it really shouldn't ruffle anybody's feathers. Even if that thing
seems to cost a lot.
Consider the sheer cost of tools required to work with both metal and wood. Circular saw, table saw, router, compound sliding miter saw, jigsaw, drill, sheet metal break <-- not a small item in terms of space.
You could spend a couple of thousand dollars in tools (I know because I have) towards having the proper equipment to build something at a proficient level that would equal something you could simply buy and have in hand in a week or two.
And that's not to mention how long it would take you to get proficient with those tools you just spent a mint on.
So, if you're able to build your own "thing" to meet your own requirements, awesome. If not, there are alternatives out there and you're free to explore those options. And that's cool too.
A sorta/kinda/maybe related story:
I had an argument with a guy on NAXJA about why I couldn't fab up a metal bracket and create a lift assist device for the hood of my XJ. This device costs around 60 bucks and one guy was just blown away that I preferred to buy one rather than run around to different parts stores or junk yards searching for the right sized lifting cylinder.
I have better things to do with my time...