My rough suggestions for starters (only A roads)
H Cafe (easy meet and good place to wait) - Abingdon - A34 - Witney - Burford - Cheltenham - Gloucester - A40 - Ross on Wye - A49 - Hereford - Leominster - A44 - Crossgates (near Llandrindad Wells) - Newtown - Welshpool - A483 - Blaenau Festiniog - A470 - Bewtsy Coed - A5 - Bangor - A55 - Conwy.
Have a look and modify if great places to stop or must ride roads not on here.