Hey Arpit, You can follow this route for 10 Days itinerary : Delhi or Chandigarh ->Mandi (Prashar lake trek -2 days) -> Parvati valley (5 Days) ->Manali ( 3 Days,skiing,paragliding ,rafting). You can also go to Dharmshala (Macleodganj,Naddi,Dalhousie,Khajjiar,Triund trek).
Hi arpit!! you can actually visit quite a lot of places. but do keep in mind that its going to be damn cold.. thought it should not deter you from going and enjoying. you can travel from chandigarh to manali. visit hidimba temple, vashisht kunj( hot water place ) and also do some activities in solang valley. u can visit rohtang pass which is going to be a days trip. one day you can just chillax in manali. from there u can go to kaza and spiti ,although unlikely that the roads will be opened during that time. you can visit dharmshala. at the end you can possibly go to shimlawith local sight seeing .
Himachal !! there are a lot of places to discover, you have sufficient tyme in your hand, you can go for Dharamshala-Mcleodganj for 4-5 days, and rest of 5 days you can go for Kasol-Tosh.. Or you can explore manali
Spiti it is
day 1 delhi- chandigarh , chandigarh - recong peo
day2 reckong peo - chitkul
day3 chitkul
day 4 stay chitkul check out kalpa rakccham
day5 come to reckong day 6 reckong to kaza
day 7 kaza and checkout near by
day 8 kaza
day 9 kaza shimla
day 10 shimla delhi