Learn Italian: Ci sono problemi con i lucernari di vetro. - There are problems with the glass skylights.

The rule for masculine nouns ending in -io depends on where the stress falls. In the singular lucernario, the stress is on the a (lu-cer-nà-rio). Because the i is unstressed, the plural just ends in a single i: lucernari. If the i were stressed, as in zio (uncle), the plural would have two: zii.

Wait, why is it i problemi? Doesn't the singular word problema end in -a, making it feminine?

Problema is a masculine noun, despite ending in -a. Many words derived from Greek follow this pattern, such as il sistema and il programma. Because it is a masculine noun, its plural changes the -a to an -i, resulting in i problemi.

Why is 'glass skylights' translated as lucernari di vetro instead of using an adjective?

Italian doesn't usually use nouns as adjectives the way English does (like 'glass' in 'glass skylight'). To say what material an object is made of, you use the preposition di followed by the material. So, 'glass skylights' becomes 'skylights of glass' (lucernari di vetro).

Could I use instead of here?