The DIY shredder it is not a strange idea. It can be done, except that it is not easy to make one that works well and, well it goes, will never have the performance of a electric shredder or burst. It is therefore a question of whether it is worth it.
The things it takes to build a DIY shredder they are a cutting disc or a toothed wheel, a number of gears to make a gear motor of sufficient power, bearings and not a little more. Obviously you also need good knowledge of mechanics, but if you came up with this idea, perhaps you are not lacking. In the end, the expense will not be indifferent and security well, you have to guarantee that yourself.
In gardening shops you can find mechanical shredders equipped with toothed blades that do not cost much and move easily because they are mounted on wheels. But we're not doing DIY here anymore and you'll need good hands. And then they are good for the leaves, even the fibrous ones (which is excellent because sometimes this material mixes the shredder) but not for the largest branches.
In the end, in my opinion, the most sensible choice is the purchase of a electric shredder. I say electric because it is easier to manage than a petrol engine (no petrol tanks and less noise) and looking at the latest models of the good brands, the power of the electric is more than enough to manage even a large garden. The speech changes if you have professional needs, but only in this case.
Personally the shredder I put it among the essential tools when you have a garden with hedges and some plants. Enough with the piles of cuttings, which you never know where to put them, and above all, enough with the branches in the trunk of the car back and forth from the landfill (which is also not a good thing for the environment). Furthermore the shredder it is useful in the preparation of home composting because the shredded is excellent for lightening the soil.
But don't get carried away. Not everything has to be shredded, the smaller branches are great for starting the fire in the fireplace (you can do without the lighter tablets) and putting aside some bundles is a good thing. As long as you have a fireplace or a wood stove of course.
If you have read this article maybe you are interested in another one: Bosch electric shredder