It goes on it's back. The glass door that would normally go on top (ie the front) is left off when you make it. Yes as snow pony says, it does need a lid. Hamsters are amazing escape artists. They can build a big pile of substrate in one corner and climb up it then hang on to the bars.
So don't put low substrate in to avoid having a lid
The deeper the substrate the better. At least 6 to 8 inches - then they can dig tunnels. Because the height is a bit limited in the detolf, some people have one end extra deep for digging, and still have a good depth in the rest of the tank.
There are a number of tutorials around for making lids - on youtube. You can get pieces of wood cut to the size you need at a hardware store, if you have the measurements. Most people make two lids rather than one big one, as they are easier to handle and you only need to take one half off sometimes.
So each lid would be a frame of four pieces of wood. They can be tacked together with nails or you can buy small metal angle joiner pieces that just screw on and hold them together (Erin's Hamsters video shows those). Then you buy mesh (and can have that cut to size in the hardware store too possibly). That can just be stapled onto the wood frame.
The Erin's Hamster video for making a detolf lid does actually give all the measurements you need for the wood as well - but I've heard it is not quite correct. So best to measure yourself, as it may depend on the depth of the wood strips as to how long they need to be. But as an example -
If the interior of the detolf is, say 160cm, you would need four long pieces of wood a fraction under 80cm (ie half of 160cm with a big of wiggle room for them to sit next to each other). You would then need four short pieces of wood to sit between the ends of each pair of long pieces. The measurement for those would be: The interior depth of the detolf minus the width of both long pieces. So if the interior depth was say, 42cm, and the long pieces of wood are 7cm wide and you have two (one for each side of the frame. Then two would be 14cm and you take that 14cm off the 42 cm leaving a fraction under 28cm for the length of the four short pieces. ie 28cm with a small bit of wiggle room to fit between the two long pieces. Those aren't exact measurements - you'd need to measure inside the the detolf.
The depth of the short pieces doesn't matter if you do it that way, just the length of them.
The lids then sit just inside the detolf on top of the bars.
One of the advantages of a tank style like that, is to be able to have deep substrate because it's one of the best things you can give a hamster. They like to tunnel and burrow and move it around and bury things in it.
That might sound like a lot of substrate - and it is initially. But the more you have, the less you use each time. When it's deep like that you can just spot clean mostly as most of it stays clean and dry. ie take out the odd handful of wet substrate and replace it and mix it in so it smells familiar. That way you only need to do a "big" clean maybe 2 to 3 months or even less. Even then, you can replace half or two thirds of the old substrate (the clean half or 2/3) by keeping it to one side, wiping out the tank, replacing it, then add the new third and mix it all in.
Erin's Hamsters has a good video on that too (cage cleaning tips).
So have linked them to give a better idea. But I wouldn't rely on the exact measurements given for the lid-making.
https://www.youtube.com/watch?v=5jVnEjrXbww&t=205s
https://www.youtube.com/watch?v=UYzDeSBE1hI
This is another video showing how she cleans the detolf.
https://www.youtube.com/watch?v=Bo44ombbC6k
If you are getting a detolf it would be a good idea to buy substrate in bulk. Hemp and Fitch are sold in bulk. Fitch is very popular on here. It's recycled food grade paper and can be bought quite cheaply in 10kg or 20kg bags. It's a bit like Carefresh but better
No dust. The 20kg bag works out a lot cheaper. It's quite big though and needs storing indoors. But it would go down quite a lot once you've filled the detolf. The 10kg bag should last a few months though.
https://www.fitchrecycling.co.uk/fit...bale-20kg.html
https://www.fitchrecycling.co.uk/ani...-delivery.html