Experts have spent the last few days removing improvised explosives which were left by the radicals who seized the building in May.
Footage from AFP shows the bullet-ridden walls of the church with destroyed icons and other parts of the building scattered on the floor.
Speaking to charity Aid to the Church in Need of plans to restore the building, Bishop Edwin dela Pena said: "More than the cathedral, what is more important is to restore the Christian community and its good relations with Muslims living in Marawi."
The extremists known as 'Maute' and inspired by Islamic State are reportedly down to 30-45 members from its original 200.
They still control an estimated area of 600 square meters in Marawi and continue to hold about 56 Christian hostages, including Marawi Prelature's Vicar General Fr Teresito "Chito" Suganob.