There is one thing you got to take note, ID who only provide ID service, some of them are really good in drawing but very weak in make the ideal to real, what i mean is, you can get a perfect drawing, but when come to real life, once you ask a contractor to make their ID to real, some of the thing are not "doable" coz those ID may not have a real experiance to study how to make those thing come true, just a silly example, they can draw a pcs of cabinet in the middle of house without touching any ceiling, floor or wall, but this is not able to work in real life (of coz i know none of the designer will do that) or some of the Ideal cost you a huge 1 to make it, eg he is actually proposing a really expensive material to do that thing but you may not know until contractor side.

So, before engage an ID, must knowing them well, not only in term of how good is their drawing and ideal, but also their experience and knowledge of material.