When I make a porch with a roof over there's this weird little line of floor tile??? but i cant delete said floor tile because there's you know stuff above it

the blue build mode arrow is pointing to it

You mean the brown line just below the roof, along the grid? That's supposed to be there, it's the edge of the floor/ceiling/roof, and sometimes unfortunately shows. You can hide it with CC or use a default replacement for the edge if it's bothering you.

There's a few replacement textures here:
https://www.feenwald.de/en/specials...s/flooredge.php

https://modthesims.info/d/459833/fl...ety-pack-1.html (there's an invisible version too, I think)
https://modthesims.info/download.php?t=459824 (and needed mod)

You should be able to delete those floor tiles if you don't like the look - it seems there is only the roofwall above them? Unless you have something sitting on the floortiles in the attic.
Deleting them will leave the view open into the roof space, of course, and you won't have a ceiling above the porch.

Otherwise, an edge hider object or a nicer floor-edge default (as linked by simmer22) is the best you can do about it.