im installing 3/4 inch amendoim in a house. i did the front of the house, no problems, but the second half of the house is an addition. the problem is that the second half of the house needs 3/4 inch plywood (roughly 450 square feet) to level with the first half, however once i put that down, the hardwood will be rasied up above the sliding glass door trac or aluminum rail. you will be able to see the side of the floor when walking in to the door. i thought about some how tappering the sublfloor down so that it meets more evenly, or perhaps some how raising the aluminum lip. any suggestions, appreciate the input.

Just thinking out loud, I'm a newbie myself, but is it worth it to buy that much money worth of plywood to even out the floor? Or would it be better off to just have one of those pieces of trim between the two sections that lets it step down?

Your options are:
1) install the 3/4" plywood as you proposed. Then at the slider, install a 3/4" reducer down to the door threshold.
2) Don't install the 3/4" plywood and where the two different heights meet, install a reducer down the the lower level.
3) Gently feather down over a 4 ft. span to the lower level using different thicknesses of plywood and felt paper.

IMO, # 1 is preferable.

Use an endcap molding, or sometimes called a baby reducer.