This all depends upon where you live, what the weather conditions are and your knowledge of minimum safety standards (code).

As a GC, I could build something that would be safe because I have the experience. As a novice, are you taking into account snow load, wind shear, uplift and other various weather situations? Roof slope? Drainage? You've now created an impervious area that depending upon your lot size vs. your current impervious coverage percentage, may exceed local regulations.

Additionally, attaching posts to deck joists, then adding a roof creates a completely different load on those joists. Typically, posting up for a deck roof, especially a detached structure, would have those posts carry all the way down to concrete piers where the piers are the proper size and depth for your local conditions.

One awning I built many years ago at the back of a house was listed as being in a 120mph wind belt. That required stronger and more connections. I wouldn't have known had I not made drawings and submitted them for the permit.

So, no, your plan is not okay. You need to get with your local building department first.