Should I stick with my Stolen (brand) BMX or should I build my own bike?
Gianis.

I'm an old man, but I used to ride BMX street and flatland years (decades) ago.

Because of their very specific geometry, Flatland frames are not great for anything but doing tricks.  If you need a general purpose bike for transportation and whatnot, stick with your Stolen (brand) BMX.

For those wondering, "Stolen" is the name of a BMX equipment manufacturer.
http://www.stolenbmx.com/