Help flowers on a cake

Previous posts from other brides got me thinking. I had exactly what I wanted to decorate my cake in my head but now I don't know if its possible I want to use white roses w schwartwalder callilies Mostly the callililys to decorate my cake.
Has anyone usedthese flowers before??
I'm worried I read they were poisonous. I really don't want to pay extra for sugar or gum paste flowers n