Re: critique my idea for a shed/gym
You've got a 5 X 8 area for a power rack and weights, and nearby an 8 X 8 Oly platform. For a one-person gym, this is overkill ... I've got my rack on a tongue sticking out the back of my platform.
For a 2 or more person gym, you'd have a better use of space to strengthen the whole floor as if it were a platform, and set up the rack and a designated OLY lifting area side by side along the long wall. If you put the rack in the corner, you'd maximise free space ... and putting your weight tree etc. between the rack and the Oly platform would separate the space well enough.
I'n this small a space, I'd be reluctant to have the floor chopped up into separate heights - e.g. Oly platform higher than the rest. You'll probably find it much more functional and flexible to keep the floor all the same height, even if you choose to insert a strip of wood in your designated Oly area to stand on. In practice, I haven't found at my modest level of lifting, that the rubber mat floors are any less optimal for cleans etc. than wood ...