Nouns:
* -er: A person who designs something. (designer)
* -ing: The act or process of designing. (designing)
* -ment: The act, process, or result of designing. (designment - less common)
* -ate: A person who designs something. (designate - used more as a verb, but can be a noun)
* -ation: The act or process of designing. (designation)
* -ee: A person who is being designed for. (designee)
Verbs:
* -able: Capable of being designed. (designable)
* -ed: Past tense of the verb "to design". (designed)
* -ing: Present participle of the verb "to design". (designing)
* -er: Comparative form of the verb "to design". (designer - less common)
* -est: Superlative form of the verb "to design". (designest - archaic)
Adjectives:
* -ful: Full of design or characterized by design. (designful)
* -less: Without design or lacking in design. (designless)
* -ed: Having been designed. (designed)
* -ing: In the process of being designed. (designing)
Other:
* -wise: In the manner of design. (designwise)
* -ology: The study of design. (designology)
The specific suffix you choose will depend on the meaning you want to convey and the grammatical context of your sentence.