。
My father's hobby is growing roses.
Literal
Father's hobby [topic-は] roses [object-を] cultivate thing [copula-です].
~ことです nominalizes the verb phrase for use as a predicate: 'his hobby is the act of growing roses.' バラ ('rose') is typically written in katakana. 栽培する is a formal suru-verb for 'to cultivate.'