Guess that all depends on your comfort level with the architect plan = necessary/good idea? Sometimes a designer can be beneficial in perfecting a design that you may prefer yet just don't think you can accomplish on your own. Selecting a furniture type, interior colors, room arrangements, convienience, etc can sometimes be a daunting task and assistance from a professional designer can be of some benefit, while other times a simple "do it yourself" design is very suitable and less expensive. I am not sure it is necessary to secure the services of a designer and an architect at the same time unless you are unsure of the architects ability to draw proper plans and provide suitable space/areas for desired decor.

That being said. I am sure there are those that would not undertake a major remodel without the assistance of a designer and I am certain designers will tell me I know not what I am talking about. So the decesion is yours to decide. You must only satisfy yourself and not necessarily the ideas of friends eventhough they mean well. Perhaps your friend does not feel comfortable in desiginig such a space, thus the suggestion, do you? You have now answer your own question. Good luck in your decision.

If you are going to be using a designer, there are advantages to starting to work with them now. For instance, if you deside that you want a light fixture hung in the middle of the room, if you are going to fill one wall with built-ins, the middle of the room changes. You would have to have the electrician rewire, spacle and paint again. Sometimes a designer can specify window treatments that would cover window trim that you decided to up-grade to mahogony. Or, some times you might frame so as to hide the tops of curtains. That's much harder to do latter. A designer might have better ideas as to where to place, or size windows so that you will have room for proper furniture placement. Making windows start 8" higher might make it so that you can place furniture agains that wall. There are probably a dozen other examples, like these, that you can't think of in advance of knowing what you are doin with the space.

All this only holds true if you have a good, experienced designer. A bad one is only a PITA, or a pushy salesman that you are commited to.

Thanks for the comments, freedee and jrice. I plan/hope to trust my architect but not everyone is good at all aspects. It was more along the lines of freedee's suggestions that I was thinking of having a designer review the plans. It's an exciting prospect and I'm looking forward to the process. I know; ask me again next spring if I'm still excited!

I had an architect draw up plans for my 2 story addition. I got so excited about the prospect of buying new furniture for my soon-to-be larger LR that I took the plans to my cousin (who is an interior designer) so she could help me with a layout that would maximize my space. Although I only asked her to lay out the LR, she offered to look at the entire design. She had some pretty good suggestions/ideas that we otherwise would not have thought of (outlets on the floor in the middle of our great room, doors swinging out rather than in, window seats for extra seating etc). Not only that, but as fredee said, we are able to direct the electrician to wire in areas with a lot of our technical equipment, my DH knows where to put the phone jacks etc.

While I wouldn't have paid for the services (as I didn't think about it from a function point of view, I was just excited about buying new furniture), in hindsight, having a designer look at the plans was really helpful.