Figure you need about 10' to be able to comfortably work under a normal car. Measure how tall your car is and add how tall you are. That would put the tip of your head under the tire. I have found that is too high to reach everything so you will probably have it 6" lower.

Sideshow and anyone else contemplating altering their building structure;

DO NOT alter roof trusses based on advice from a carpenter or contractor!

The design and analysis of trusses is very complex and unless a professional engineer has provided the alteration design for you, you are likely to create a safety and liability hazard for yourself and all subsequent owners of the property.

The zoning laws of you're community might even prohibit making that kind of alteration without a PE design. Ask your Building Inspector.

NO contractor or carpenter is knowledgeable enough to know how trusses are designed unless he is a drop out from the structural engineering profession..

Any fool can use a saw and hammer and butcher the structure and say it was (physically) easy, but it may be a time bomb waiting to collapse.

Don't take this lightly. There are lawyers standing in line just waiting for this opportunity.

Another consideration that many won't realize is that house builders rarely compact the soil when they backfill inside the foundation. The soil under the slab along the foundation walls generally settles a bit through time and there is often a void between the slab and the soil. I have seen a void of about 4" in one job that I investigated.

The condition is often unknown because very little load is applied along the edges of the floor when the vehicles are out in the parking areas.

Due to cramped spaces I would guess that many a lift has some of their posts bear near the edges of the floor, right where the soil has settled, thereby causing cause for concern. If/when that piece of concrete breaks under the load, it will be an alarming if not dangerous situation.

It would be good for potential home users to try to determine if the post base locations are on sound bearing by sounding or coring a hole in an adjacent similar location.

I agree this does sound like a really good idea

i have scene plenty of engineers screw things up.... just because its drawn on paper doesn't mean it always works, and you dont have to be an engineer to modify a simple roof truss, just have some common sense,
think a fabricator designed the new fords so that when it needed a head gasket you had to remove the cab? doubt it

Engineers do make mistakes, but atleast they are not from ignorance.
If you have a sealed drawing from an Engineer, and it falls down and ruins your car or kills your child, he is responsible and pays the price or goes to jail, Not You.
Do you drill your own teeth? Do you do your own heart surgery? Those only involve a grinder or a knife.

You DO have to know how to do a statics analysis to modify a truss.

Go into any auto shop. They generally have one four post(Alignment rack) and 20 2 post. A 2 post gives you so much more room to work. There really isn't much you can't do if you have a screw jack.
Now if you are going to use it for storage primarily and work on the car once and a while then a 4 post is going to be much easier to get the car out of the way quickly.

I ended up buying a few of these:http://www.kennan.ab.ca/lifts.html

Set up in some extra space in a warehouse, they seem to work well. Solid enough, well thought out. Don't really roll so easy with a car loaded on them, but not bad with enough guys.

LOL The Titan hobby lift IS THE SAME EXACT lift as my eagle. Linkage, locking mechanism etc... everything is the same. I love mine.

But where is the Eagle made?

Before I bought a bike lift, I asked Eagle about theirs because it looks just like one of the US made Handy Lifts, which is one of the Industry Standards.

It turns out that Eagle's was a China copy. So just because it looks the same, don't jump to conclusions.

I put their literature in the trash.