C++: Smart Pointers & Fluent Design Pattern with References

I'm trying to learn C++ after being spoiled with high-level languages for all of my life.

I would like to use the fluent design pattern with a class, but I'm worried that I'm making a mistake somewhere and sacrificing performance.

Say that I have a class Builder, and it has some member properties and methods. All of it's methods look something like so:

Builder &doSomething(SomeTypeThatCouldBeAClassOrAPrimitive &thing)
{
    // do stuff, such as
    // modify a class member
    memberThing = "something";
    
    return *thing;
} 

And say that I'm using it like so:

unique_ptr<Builder> builder(new Builder());

builder->doSomething(someVal)
        .doAnotherThing(someOtherVal)
        .doAFinalThing(someOtherOtherVal);

Just from the code provided, am I doing something wrong, or could something be done more efficiently?

Please let me know if I need to provide more information.