According to The Canadian Press Caps and Spelling textbook, the spelling of roller skate changes depending on the context.
Here’s your lesson. Now pay attention, children…
What does this mean?
“I am going roller-skating.” The term roller-skating is a verb, and therefore should be hyphenated.
“Where are my roller skates?” The term roller skate is a noun, and therefore should be two words.
By this rationale, “I am going rollerskating,” is also acceptable when using the term as a verb.
NOUN – two words
VERB – hyphenated or one word