Home Depot runs that No Interest, No Payments for 1 year deal all the time when you spend over $299. Didn't you get that deal for the 1st purchase?
Wish you lived closer to me, I just had a whole pile of shingles left over I could have given you.
Can you go to Lowes and open a card with them? They should give you a few hundred $ credit limit AND 10% off your first purchase. At least to get that roof replaced as fast as possible.
If it was my house, I'd take those trees down around the house. Shade and debris from trees can take years off the life of a roof. I had one building with a beautiful maple next to it and we all loved that tree, but the roof was covered in moss and every fall the leaves took days to clean up. We finally had that tree taken down (75' tall) and everybody loves that it's gone! More light, cleaner and now I will have the roof replaced next year without all that moss growing back and rotting out the trim.