Qualities can be compared using special forms of adjectives (and adverbs). These are called the comparative and superlative forms. Thus, for the adjective groß:
positive degree: Mein Haus ist groß My house is big comparative degree: Dein Haus ist größer Your house is bigger superlative degree: Ihr Haus ist das größte Her house is the biggest
Naturally, some adjectives or adverbs, such as sterblich, einmalig or absolut, have a meaning which excludes any possibility of comparison, and there are other ways of indicating degree, for example by modifying the adjective or adverb by an adverb of degree like sehr, see 7.4.