It sounds rather industrial to me. Do you need to garage more automobiles or, like me, more other stuff?
I would reconsider the shed, giving it a concrete floor, loft storage and double doors for large-item access.

The thought process was that the detached garage would add more long-term value to the property than a shed in the back yard. While I don't need it for cars, a future buyer might.

The other problem is that my entire lot slopes to one corner, so any concrete slab is going to have to sit on a foundation. The sites on my lot able to accommodate a shed are more sloped than the garage site at the end of my driveway, requiring many courses of block and a lot of fill. To top it off, there is no good access for delivery vehicles to the area behind my house. The bottom line is that a comparable 16x24 shed, without the brick exterior, was almost as much as the detached garage due to the extra materials and labor.

I am still considering building a small retaining wall in the back, filling it in, putting 4" of crushed stone down as a base, and having a shed (with wood floor) built on top. Not nearly as nice--nor versatile--but probably under $10k.

JKG

What about taking the money and putting towards rental of a storage facility/unit?

I think you're right that building a garage will add more value (or subtract less--not sure how many people need 4 garage spaces) than would a shed. The sf price seems quite reasonable, although that all depends on your locale.

I have considered a rental storage unit, but most of the things that we're storing need to be readily accessible at the house (lawn equipment, etc.)

I don't need 4 garage space either, and have considered turning the second space in the proposed building into a finished workshop or office. That would perhaps be more attractive to a buyer, but also raise the cost of the project somewhat.

I would estimate that roughly 50% of the homes in my neighborhood have a 3 car garage, either integral or attached. There is one home which has a 2 car detached garage behind the house. When we built our house, we opted for the integral garage in part because it presents a "cleaner" image of the house from the road. Obviously, a detached garage at the end of our driveway would negatively impact that image, though it should be no worse than having an attached garage with the doors facing the road.

JKG

For what it's worth, we built a detached workshop/garage even though we knew we didn't need the extra garage bay. We even installed an oversized door to insure it would accommodate (someone else's) larger vehicles or boats. It seemed like the prudent thing to do both for resale value and any unforeseen needs (e.g. storage, hobbies, etc) in the future. Instead of parking a car or boat in it, we decided to add HV/AC and stain the concrete floors, and then buy a pool table. WeÂve always wanted a pool table but never had enough room for one in the house. Properly insulated, garage bays can be very versatile. If building codes allow, someone could even convert it into a guest house down the road. But then the lots are large and outbuildings are pretty common where I live.

Those bids sound in the ballpark. I've heard that garages are typically $50/sq ft, and brick will increase that price. Last fall we looked into building a ~30x40 bricked garage with upstairs unfinished storage (could be converted to living space) and got estimates around $75K. That squelched that idea until my DH teaches himself masonry. :-)

Who needs a 4-car garage? We certainly do, since I'm married to a mechanic and wanna-be farmer who owns a tractor and a growing collection of tow-behind implements. Of course, our lot is 7 acres, which almost guarantees that yard care equipment needs go beyond a walk-behind mower.