There are many types of patio covers style, I’ll try and cover the most common. There are couple basic thing all covers require. Footings, Post/Beams, Roof (Solid or lattice)
What is the purpose of the footing?
The footing will carry all the loads of the cover. A footing is not the same as a slab. The slab is just the finish top and is not made to carry really heavy things.
If you have concrete already, is more like you just have a slab. And not a footing.
What can happen if you place the post on top of slab? It can crack the concrete, and patio cover sink.
How do you know if you have a deep enough footing? There are a couple of ways to find out. One would be digging on the side to see how deep it is.
Second would be using a drill bit long enough to confirm concrete is the required depth.
So what is the required depth, is very easy. A trip to your city and asking for the patio cover pamphlet. On the pamphlet there are a couple of charts. Depending on the size it will call for the size required. Of course these are for basic patio covers, which are the most common.
If you don’t have a footing, the fix is simple demo everything and start from the beginning or just pour a pad. A pad is the most cost effective way to go. All it involves is cutting a square usually 16″x16″, 24″x24″, or whatever size needed on the existing slab.
Once you have the proper footing/pad with an adequate post base. The fun begins. Before setting post you have to figure the slope which is 1/4 per foot minimum. While still having enough headroom 80″. There are a couple of ways to meet this requirements. I like to start backwards.
Starting at 80″ plus size of beam(depends on span) plus rafter size(depends on span) plus 1/4 per every foot of span.
That number would be the clearance needed on the back, on two stories homes, u usually have enough room. The tricky part is on single story homes it gets somewhat complicated and creativity is needed. You need to make it function and look nice.
Now if your just looking for a lattice then you just need to make it level. On waterproof patio covers you need to go with roll roofing because the roof is not steep enough and going with shingles you might end up regretting. Hopefully I was available to show how a patio cover is put together.