You don't, sunshine. A few reasons why:

1. The actual chemical reactions involved are quite dangerous. A little too much X or heat Y a little too long and you and explosion with bonus toxins. This is true in a house or in a proper laboratory, but a house is not equipped with the sort of hardware to make these reactions safe under any circumstances.
2. Making methamphetamine from chemicals readily available to the general public involves altering the chemical makeup of many of these chemicals. These are reactions separate from actually making methamphetamine, which is really quite simple with access to certain tightly-controlled chemicals. None of these reactions are going to be entirely “clean”, you are not working with pure chemicals and there will be chemical byproducts that you would not expect - even if you were doing this from the perspective of a seasoned chemist. These chemicals will interfere with actually making the meth, and they will contaminate it with everything from random carcinogens to heavy metals.
3. There is no good reason to make meth at home. If it's purely for profit, the product will be crap and you will be exposing yourself to the absolute horrorshow that is small-scale slinging. If it's for personal use, then you are definitely poisoning yourself (far worse than with a “cleaner” lab meth), assuming you didn't hurt yourself during the cook. It is difficult to use meth if you've blown off a hand, blinded yourself, suffered chemical and thermal burns to significant portions of your body, dissolved parts of your lungs and/or sinuses, or done other permanent damage to yourself. I guarantee that each of these things happens, and on a regular basis, in home cooks.
4. Using methamphetamine is bad. There is some debate to be had here, people have made some great arguments as to why it can be used under certain circumstances for good reason. Even if every single one of these arguments is true, you're only looking at a tiny, tiny portion of users. Almost everyone who uses it destroys their lives very rapidly.

TL,DR

Making meth at home is dangerous. Don't use meth.

Edited for typo.

Vuoi davvero spendere qualche ora per fare qualche grammo di metanfetamina, e se sei preso puoi avere una lunga condanna.

Il metanfetamina è così economico, che puoi semplicemente lavorare ovunque per qualche ora, e puoi comprarti Meth di alta qualità senza problemi.