Buying Floor plans for a better bid

[Alexis A Peinado]

So I recently had a contractor look at a property that has a 2 car garage that I'm hoping to convert into 2 studio apartments. He recommended that I first hire a designer that will not only design it but also make sure it passes all codes. This is my first BRRRR so I'm not too sure of this step. Has anyone done this and then asked for bids? The contractor is stating that this route will give him (and any other contractors) a much better idea as to how much the project will be. The quote I got for the floor plans are 1800.