First of all, this is not a "what-song-should-i-learn-thread".

I was just wondering what the heck to play.
Im tired of just learning songs.

When famous guitarist say that they used to sit in their room and play guitar all day, what did they play? Just improvising or what?

Thank you.
Improvise, come up with your own riffs/solos. It's much more rewarding than learning songs by other bands. You should learn some songs by other bands as well though.
Gear as 2015:
Ibanez PGM401
Music Man JP6 (for sale)
Music Man Axis (for sale)
Fender American Deluxe Stratocaster
Ibanez EW Acoustic Steel string
Crappy Cort Acoustic 12-string
NI Rig Kontrol 3 & Guitar Rig 5
I doubt they sat down improvising all day, because that's what I do, and no one copies me.

Anyways, they probably learned theory and things like that. Things that you would need to become really technical.
Cam Sampbell's my hero
if you really enjoy playing it should come easy to just sit down and go crazy and just do whatever, how do you think new songs are made? not by learning other peoples songs.
i agree with joey radical here.. just make up some new stuff... make riffs and put solos on them... then you can play forever..:P
Learn the major scale of every key on every fret on the neck. Then learn every mode. I think that's what the famous guitarists did for years in their rooms.
They probably sat and ran exercises, learned other people's songs that they knew would challenge them, write their own stuff, improvise over backing tracks, learned as much theory as they possibly can. Basically anything that has anything to do with the instrument.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”