I´m pretty new to this, I´m using a foucsrite interface, and I´m wondering if it is worth it to make or buy a direct box for having a balanced signal in order to reduce noise. I don´t need a long cable, it´s just for home studio. I asume that using a direct box i would only have balanced a half of the path that goes from my guitar to the interface, so I dont know how much can that improve on cleaning noise.
It's not clear from your question whether you actually have a noise problem or not, but for standard length guitar cables (3 - 6 meters) a DI should not be necessary. You also didn't say what model of Focusrite interface you're using, but most of the current semi-pro models have a designated instrument input for guitar and bass; you should normally be using that.
To answer your question precisely: no, under normal circumstances, it would not be worth it to add a DI to a guitar input, since there would be no perceivable benefit and would introduce additional complexity, cost and points of failure (in the additional connectors required).