Thank you for the response folks. I've never had problems with snapping the said roof before and just today I had this issue. Restarted Valheim and I'm still having the same issue. Below is the screenshot:

https://steamcommunity.com/sharedfiles/filedetails/?id=2931042139

As soon as I place the roof it collapses instantly.

https://steamcommunity.com/sharedfiles/filedetails/?id=2931042139
this is the screen that youre referring to ? how far up are you even ?
try to add a support collumn underneath it that you remove afterwards or something

That isn't a screen shot link....

I apologize. I didn't copy the proper screenshot link. I've updated it.

As you can see in the screenshot, I'm only at the second attachment and it should be green since the base is blue. And I don't know if you notice but in the screenshot there's a bit of a gap from the blue roof and the one connecting to it.

Stick a beam under it but first wait a second and see if the first roof piece is actually touching the stone. Have you tried attaching it to the other side? Does seem wacky. May have to send in a bug report.

Building is fiddly and takes time to learn. The game is more interested in what you are snapping to that the item itself. Building starts with the item being blue when you look at it in hammer mode. It goes then to a couple shades of green, yellow, orange, light red and dead red. Dead red always breaks. If you don't start your architecture with the item actually touching the ground and being blue or if one beam is green and rest blue, that carries up and that one will break first. If all of this is too confusing there are some great videos on understanding the system. Watch one.

try iron it may help

A specific piece or always? And snapping to what? Need more information...

It worked perfectly fine for me just 6 hours ago. There is a support limit on how high up you can build. You might have to raise terrain a bit under the base of the structure you are trying to build or use sturdier materials than you are trying to build with.

I always build the frame for my roofs (out of beams) entirely, before putting in the thatch. It always snaps perfectly to the horizontal beamwork.

Even if you don't want to use horizontal beams at every level of the roof, putting them in first to snap in the thatch, and then deleting any beams you do not want would work (assuming they aren't needed for support).

The interior roofs all have weird snapping behavior. Try snapping it to the corner of the adjacent piece