Welcome, This is a tanky dps build of gp. Gp is the King of solo top. The reason of this build is to let people play tanky gp instead of just dps. Gp is easily aimed at team fights, so the reason of getting health is to sustain much longer in fights and prevent from dieing.
These runes lets gp burst out his "q" ability, Parrley, to enemies or minions. Parrley is a great source is harrasing enemies in Solo top, so jungles can easily come gank and kill.
Ignite and Exhaust are great offensive spells for fighting Solo top, before getting zoned or killed. Ignite lets u finish someone off without tower diving, For example, when you harass people and they're on low u Parrley once more and ignite them to get the kill instead of tower diving. Exhaust lets you slow down enemies when you're not fast enough, Or when u duelign 1v1 with someone u can Exhaust people so they take less damaage on you.
These are great spells for melee damage dealers.