Talk to a roofing contractor 1st. Not a trivial smear with tar situation most times. You need to seal all the cracks after checking for rot and termites, and making a decision if the existing membrane is sound. Some roofs after many repairs need to be removed and started over. The weight of more material would collapse the roof.
I would use roofing cement, some patching fabric, possibly some sheathing, and some tools. The tools you will need include some old rags you have and a heavy duty razor.