I have a one car garage wjth a garage door opener. The ceiling is pretty high above the door when it is in the open position. Is there a way to build a platform above the door with perhaps a ladder to the platform so I can store iems there? Has anyone seen a plan for anything like this? Thanks.

Storage areas must be designed for heavier loads than floors. Your garage walls can carry this load in 3 sides. The fourth side is no problem if you run the joists from side to side.Framing the storage platform this way also avoids placing additional load on the garage door header, which is prpobably very light.

I'd suggest having an architect or structural engineer design your joists, so that your storage area won't sag or collapse.

Richard I will agree with you on this. The only thing is professionals that you suggest cost lots. I suggest that you go for it. It is a garage and you can put up joists as mentions side to side even making a box of joists to fit wall to wall across the top. Then use screws to join it tot eh walls and if you leave a gap of say 1/16th of an inch on the outside walls and screw them in you should be fine. Too many screws however on teh outside walls can pul the wall in a 1/16th so just be carefull to keep that gap in fact use shils to keep it there.

Now as far a weight that this will hold. Do you have 2x4 construction 2x6 2x8. The higher the wall stud size the more weight it will hold safely. In the case of even 2x4 you could safely put a load of say 400lbs provided that there is not other loads on that wall. I have a canoe/boat motor/ fishing gear etc on a shelf and I am going to add too it.

There are products sold to make use of the space above your garage door that hang from the ceiling joists. They can't carry very heavy loads but you don't want to carry heavy loads up the ladder to your high storage do you? You can find them at the major home and hardware stores.
You can also make your own (see recent issues of Family Handyman magazine). One design is simply making a "T" out of 2X2 and 2X4s and fastening several of them to the garage ceiling joists just far enough apart to slide in plastic storage tubs with lids. Hope this helps!