oh my gosh..this is exactly what DH and I want to do to our garage...then the old living room will be my sewing room and the 2 empty bedrooms will be a guest room and a storage room!

When laying out space, there is a tendency to place tables and furniture along the walls and neglecting the center of the room. There is also the tendency to leave wall space unused. Be sure to play with paper and pencil and work with T formations, where one or two tables jut at 90 degree angles from a table or wall.
One suggestion is to place two work tables parallel coming out from a side wall and leaving about 3 feet in between. On the wall between the tables, you could hang rulers and catchall containers. Use one of the tables for cutting and one for ironing and "spreading." Just be sure they're high enough for you to cut without leaning over!

One further note- a design wall can be fully movable if you use a large piece of insulation board covered with flannel. That way, valuable wall space can be used for shelving and the design wall can lean against an area you don't have to get to often (a hot water heater closet?)

Depending on Size of Garage.... take in to consideration, Tables that can be Folded and Put away in a closet. Tables that you can be moved easily away from the walls, tables or work center, storage for machines not in use, area for notions, nice Storage for Fabric with plenty of shelves or bins or tubs.
Lighting is important... I like natural light near windows.... flooring that can be easily cleaned, dust mopped or Vacuumed, plenty of outlets or another Circuit/fuse box may be necessary for every thing that will be plugged in,,, I agree with several other posts that you need to make a list of every thing you are going to need as well as hubby's list too... Can't wait to see pictures....

Put all plugs at a chair rail hight along wall if possible. It makes it easier to plug in machines both sewing and computing.

That was my sewing room in our old house. I had two closets (actually one closet with two french doors) all along one wall - great for storage of fabric (my 3/4s of the space) and office stuff (hubby's area). The rest of the area was open. We did have the mechanical stuff in the garage as well (furnace/water heater/water softner). We had partitioned off an area about 7 foot by 14 for that. It was marvelous because one wall of the utility room area was shelves for pantry storage. This is a photo of just half the closet. I calculated one time that I had almost 900 yards of fabric in that closet.
[ATTACH=CONFIG]341531[/ATTACH]

What a great idea! One reason I love having a corner of the living room instead of the extra bedroom is so I can be with hubby in the evenings after the babies go to bed. If you have an ikea nearby, the expedit shelving makes a nice room divider that is low and great storage.

Thanks for the link. I hadn't seen this subforum before.

How wonderful that your hubby wants to share the space and you have found a big enough place to do that.

Another suggestion: Place your fabric in an area(s) where it won't be exposed to light (because it will fade.)