In reply to Paul Robertson: I did it as a loop 2 years ago, much further and harder work than doing it in a straight line. I took 17 hours but I was 61 yrs old at the time! It is about 54Km with over 5,000m of ascent.
I started from the Climbers Club Hut Ynys Ettws in the Pass but if starting from Pen Y Pass a good way is:
Crib Goch, Gardedd Ugain,Snowdon descend from Clogwyn station to Nant Peris. Up Elidir Fawr, Y Garn, Glyder Fawr, Glyder Fach, up Tryfan. Descend Cwm Tryfan (easier going than the West side) to the A5 at the West end of Lyyn Ogwen. Go straight up North to join the Cardeddau ridge West of Cardedd Daffyd (Leave this top plus Pen Yr Ole Wen until later). Go over Cardedd Llewelyn, Foel Grach, Garnedd Uchaf, Foel Fras. Return along same route but do the Outlier Yr Ellen by contouring across from below Carnedd Llewelyn. Climb Carnedd Daffydd, Pen Yr Ole Wen and descend to Ogwen. Return to Pen Y Pass via Lyn Bochlywyd and over the Col between Tryfan and Glyder Fach and contouring back to Pen Y Pass. There are other permutations and it might be worth doing it in reverse as the flog UP Elidyr Fawr was grim, boggy and slow. Better to go down this way.
Good luck!