Learn Polish: Na dachu siedzi jakieś ptaszysko. - Some huge bird is sitting on the roof.

The root word is ptak (bird). To make it an augmentative, we add the suffix -ysko. When adding this suffix to a noun stem ending in k, the k mutates into sz. This is a common consonant shift in Polish, giving us ptaszysko.

Does ptaszysko just mean the bird is physically huge?

Not necessarily. While they do indicate large size, augmentatives ending in -isko or -ysko often carry a pejorative (negative), creepy, or threatening tone. The speaker here might be slightly intimidated or annoyed by the bird, not just neutrally describing its wingspan.

Since ptak is a masculine noun, why is it paired with the neuter pronoun jakieś?

When you add the -isko or -ysko suffix to a noun, the new augmentative word becomes grammatically neuter, no matter what the gender of the original noun was. Because ptaszysko is neuter, it requires the neuter pronoun jakieś instead of the masculine jakiś.

As a quick refresher, why does dach take the -u ending in na dachu?