Hi, I personally didnt use an ID when we did up our resale couple of months back. Sometimes, people use ID for convenience as they don't know where to start. For us, not having an ID makes the entire project more fun and definitely more "brainstorming" together in putting our ideas together. Got a contractor to do the hacking, floor tiles, parquet, toilets and carpentry. Results were good and many friends who came by asked who our ID was. An ID is good in doing the mock up/3D drawings for visualisation but I was also surprised when the carpenter drew up 3D when we told him our requirements for the wardrobe and cabinets. Since your flooring is already done, perhaps it will largely be on carpentry, lighting and maybe toilets? Shouldnt cost too much unless you will be heavy on the carpentry works. Let me know if you wish to have the contractor contact.