If you follow the route as suggested by oklodhi then here is the road conditions you will have to face for your journey.....
Islamabad-Mansehra:
Good road condition but traffic is high
Mansehra-Balakot-Naran-Jalkhad:
Good road condition with a few small patches of bad road due to landslidings. In fact the road from Naran to Jalkhad is the best road of the entire Kaghan valley.
Jalkhad-Behsal-Lulusar-Gitidas-Babusar-Chilas:
No road whatsoever. You will be travelling through glaciers, water streams, stones, gravels, etc. The proper carpeted road starts almost 1 hour before Chilas. Also near Chilas there is a point from which KKH and Indus river is visible and the total time form his point to KKH is not more then 5min. but due to land sliding one need to take a very long route through the Chilas main Bazaar and you will reach the same spot after one hour!!! of driving....
Chilas-Astore-Rama:
After Chilas you will be travelling along KKH for almost 3 hours and enroute you will pass Raikot Bridge which is the starting point for Fairy Meadows.
The road from Chilas to Raikot is just reasonable but after Raikot there is absolutely no road till Gilgit!!! Fortunately you will turn just before the town of Jaglot towards Astore. From this point onwards the road upto Astore is very good. From the main Astore Bazaar a road turns up towards Rama. It is almost 10KM and the road is also very good.
Astore-Chilam-Deosai-Skardu:
Astore to Chilum the road is in good condition and runs along a very beautiful and Green/Blue Chashma (After Gorikot).
Chilum to Deosai is pure 4X4 but the mud track is not so much bumpy and you will enjoy.
Barapani to Sadpara/Skardu:
Absolutely awful. You will be driving on gravels and stones and it seems to go on and on and on......
Skardu-Shigar:
Wonderful black top road passing through desert......
Skardu-Kachura:
Good road.
Skardu-Chilas:
From Skardu to KKH it is almost 160KM. The road is in descent condition but it is a very dangerous road. On one side is mountain while the other side river Indus flows.... The road is narrow and on most of the occasions one vehicle has to stop to allow the other to pass bye.....
I hope this review of the roads might be helpful to you and will give some idea as what to expect.....