Interesting question. I assume the top would be meshed? So there'd be light from the top. I personally think they do need a side they can "see" out of or smell out of, even though they don't see well - so they can interact and get your attention. A hammy could get a bit depressed if they couldn't communicate with you easily, eg by coming to the bars/perspex to let you know they want to come out. I also think, as it would be darker, they may sleep more as if it's a big burrow, but that is just a guess.
Clear sides do help owners monitor a hamster as well as see them/interact with them.
I am not a great diy fan either but with that Metod unit I think you would need mesh or perspex on one of the sides and a meshed lid. The height would be 37cm which isn't that tall for a tank style when you have say 15cm of bedding in but it would be ok for a dwarf hamster (too low for a syrian wheel probably).
Have you see the video for the Linmon cage?
https://www.youtube.com/watch?v=Ocdcl-82ybE
Also, what country are you in because sometimes diy cages don't end up that cheap and there may be a better cage you can buy for less money.