Voluntary Hajj on Behalf of Deceased Parents or Giving Charity?
Question

Is it better for me to do Hajj on behalf of my deceased parents, knowing that they had done the obligatory Hajj, or to give that money towards building a mosque or towards jihad for the sake of Allah?
Praise be to Allah.The best way to honor your deceased parents
The best way in which a person can honour his parents is the way taught by the Prophet (peace and blessings of Allah be upon him), which is to make du’a for them, pray for forgiveness for them, honour their friends and uphold the ties of kinship, for you have no ties of kinship except through them. 
This is what was stated by the Messenger (peace and blessings of Allah be upon him) when someone asked him: “O Messenger of Allah, is there anything I can do to honour my parents after they die?” This is the reply that he gave. 
Voluntary Hajj on behalf of deceased parents
As for doing Hajj on their behalf , offering sacrifices on their behalf , and giving charity on their behalf , that is undoubtedly permissible, and we do not say that it is haram, but there is something that is better than that, because du’a is better than that. 
So make these deeds that you want to do on their behalf on your own behalf – do Hajj on your own behalf, give charity on your own behalf, offer a sacrifice on behalf of yourself and your family, spend money on building mosques and on jihad for the sake of Allah on your own behalf. 
You will need righteous deeds just as your parents do, and the Prophet (peace and blessings of Allah be upon him) has taught you what is best and most beneficial for your parents. Do you think that the Messenger (peace and blessings of Allah be upon him) was unaware that it is better for you to do Hajj and give charity?! 
No, we can never believe that the Messenger was unaware of that. We know that the Messenger chose these four things: du’a, praying for forgiveness, honouring one’s parent’s friends and upholding the ties of kinship, because these are honouring one’s parents in a real sense. 
Prophet Muhammad (peace and blessings of Allah be upon him) said: “When a person dies, all his good deeds come to an end except three: ongoing charity (sadaqah jariyah), beneficial knowledge, or a righteous son who will pray for him.” 
He did not say: or a righteous son who will give charity on his behalf, or offer a sacrifice on his behalf, or perform Hajj on his behalf, or fast on his behalf – even though the hadith speaks of righteous deeds. 
The Prophet (peace and blessings of Allah be upon him) did not suggest doing good deeds on behalf of the deceased and suggested making du’a instead. 
We bear witness to Allah and we know with certainty that the Messenger of Allah (peace and blessings of Allah be upon him) would not have turned to something inferior and ignored that which is better, because he (peace and blessings of Allah be upon him) was the most knowledgeable and most sincere of people. 
If giving charity, offering a sacrifice, praying or performing Hajj had been prescribed in this case, the Messenger of Allah (peace and blessings of Allah be upon him) would have told us about it. 
I say to the seekers of knowledge concerning such matters where the common folk follow the inferior way, that they should explain to them and say, Show me a single text in which the Prophet (peace and blessings of Allah be upon him) enjoined observing a voluntary fast or giving voluntary charity on behalf of one's parents. You will never find one. 
Rather he said: “If a person dies owing obligatory fasts, his heir should fast on his behalf.” The Prophet (peace and blessings of Allah be upon him) enjoined observing obligatory fasts on behalf of the deceased, not voluntary fasts. 
Search through the entire Sunnah from beginning to end; can you find any mention that the Messenger (peace and blessings of Allah be upon him) enjoined giving charity on behalf of one's parents, or observing voluntary fasts on behalf of one's parents, or performing a voluntary Hajj on behalf of one's parents, or spending money on the public interest on behalf of one’s parents? No, you will never find any such things. 
The most that can be said is that the Messenger (peace and blessings of Allah be upon him) approved of this, and approval of a thing does not mean that it is encouraged in shari’ah. 
The Prophet (peace and blessings of Allah be upon him) approved of Sa’d ibn 'Ubadah when he asked for permission to give his garden as charity on behalf of his mother, and said, “Yes.” He (peace and blessings of Allah be upon him) also approved of the one who said, “My mother has died, and I think that if she could have spoken, she would have given charity; can I give charity on her behalf?” He said, “Yes.”
But did he command his ummah to do voluntary acts for the sake of Allah and give the reward to the dead? This is not the case, and anyone who can find such a report, let him tell us about it. The only exception is obligatory acts, for what is obligatory must be done.” (Fatawa Ibn Uthaymin, 21,267) 
And Allah knows best.