Tell me what you think about my plot idea for a novel?

It's about someone called Travis and in the story everyone and everything is a figment of his imagination. In the story the characters from his imagination live out there life so the readers think that they are actual people. They soon end up having the same goal which is to get rid of any misery anyone would experience so they try to create a utopian world. Throughout the story Travis appears to be the antagonist and stops the characters from achieving their goal whereas in reality he is trying to create a eutopian world aswell. The characters end up going insane and have to continue assuring themselves that they are only human when they aren't. The interesting thing is that the whole book will be written in dialogue to create the illusion of what is going on in Travis's mind and I won't say where they are exactly except if it is brought up in the conversation. The thing I can't decide on is whether or not to stop using dialogue in the last chapter when Travis steps out into reality. To clarify Travis isnt dreaming and the story is that he is merely projecting his goal onto the characters. However whenever something goes wrong he kills off the character in weird ways which subtly hints that something isn't right. This soon creates the idea that there is no such thing as perfection because noone ever succeeds in creating utopia. Later on Travis gains a connection to the figments and feels he should create utopia since he killed off most of the characters. This is when the real world and his imagination clash because the barrier was him being evil in his imagination but now he's become good. Can you also add a bit of detail about what you think about the idea and how I could improve it?