This is the 1169th most frequent Polish word.
większych
"Większych" means "bigger" or "greater" (genitive or accusative plural form).
The word "większych" is an adjective in the genitive plural form, modifying "planów" to indicate their degree or significance.
Nie mam większych planów na weekend.
I don't have any major plans for the weekend.
"Większych" here is used as an adjective in the genitive plural form describing "pomieszczeń" to convey their scale.
Potrzebujemy większych pomieszczeń na to wydarzenie.
We need larger rooms for this event.
In this case, "większych" is an adjective in the genitive plural form, applied to "problemów" to denote their severity.