Delhi - Rohru route:
Delhi >> Sonepat ->> Panipat ->> Karnal ->> Ambala ->> Zeerakpur (From Zeerakpur, take the bypass and you will skip Chandigarh & Panchkula and will directly come on the new Himalyan Express which will help you enter Himachal instantly). >> Dharampur >> Solan >> Shimla >> Kufri >> Theog >> Kotkhai >> Jubbal >> Hatkoti >> Rohru.
It takes almost 5-6 hours from Shimla to Rohru and from Delhi to Shimla it will take almost 8-9 hours.
Hope it helps.
The distance between Delhi and Rohru (Himachal Pradesh) is about 422 km and it takes around 8 hours to reach there. Here are the driving directions according to google maps.