Office space contribution taxes

Hi,

In the article from the Dexxter learning center, they advise against effectively including (part of) your home in your accounts. However, you can enter 20% of all utility costs (internet, water, electricity, gas, etc.) in your accounts.

Here is the article, by the way: https://dexxter.be/drie-redenen-office-huis-beter-niet-inbrengen-als-kost/

Okay, utilities, but I use my entire garage as a fitness for customers, an office to work in, a toilet... etc. Surely there must be a way to include this? Rent it to myself or something?