I wanted to know that if for some reason you sleep through Fajr and then wake up in the morning, do you have to make up Fajr straight away or can you wait till Thuhr time and I heard that if you pray Fajr after Thuhr then you don't pray 2 Raka'h Sunnah. I'm unsure on this matter.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Whoever missed the Fajr prayer or any other prayer out of forgetfulness or because of oversleeping, has to perform it as soon as he remembers it and he should not delay it except for a necessity. This is the view of the majority of scholars and they provided as evidence the Hadeeth reported by Al-Bukhari and Muslim . The Prophet said: "Whoever forgets a prayer, he has to perform it as soon as he remembers it, and its expiation is to perform it as soon as he remembers it." Then he recited the following verse, Allaah says (what means): {And perform the prayer for My Remembrance}[Quran 20:14]" Another Hadeeth reads: "Whoever sleeps and misses a prayer or forgets to pray it, its expiation is to pray it as soon as he remembers it." [Muslim] The scholars demonstrated that since the Prophet ordered the person who forgets his prayer to pray it as soon as he remembers it, then this is evidence that it is not permissible to delay it further when one remembers it. Moreover, when one makes up for the missed prayer, it is desirable for him to make up for the Sunnah prayers as well [which one performs before or after the obligatory prayers] regardless whether he makes up the prayer before or after Thuhr. The evidence for this is that when the Prophet and his Companions overslept and did not pray Fajr prayer on time and it was the heat of the sun that woke them up, he ordered them to pray two Rak'ahs Sunnah of Fajr and then pray Fajr. [Abu Daawood] The auther of 'Awn Al-Ma'bood said: "This is evidence about making up the Sunnah prayer." 

Allaah Knows best.