Both infinitive and gerund clauses can serve as Subject Complement clauses for appropriate predicates, but as a general rule, gerunds are more common and normally to be preferred over infinitives in subject position.
My guess is this is probably because initial infinitives require a To as a parser detour marker -- i.e,
- To redo the kitchen was my idea.
- *Redo the kitchen was my idea.
but gerunds are morphologically marked and don't require a particle to keep track of.
- Doing the kitchen was my idea.
By the same token, there are rules like Extraposition that move subject infinitives from the beginning of the sentence, where they sound stuffy and uncomfortable, to their preferred end position in the sentence
- ?To redo the kitchen is a terrific idea. [==>
- It's a terrific idea to redo the kitchen.]
but don't work so well for gerunds, who are doing just fine in subject position
- Redoing the kitchen is a terrific idea. [==>
- ?It's a terrific idea redoing the kitchen.]