ledger for ceiling joist
Your design (2x10’s at 12” oc spanning 20’-8”) will support about 38 lbs. per square foot for #2s and about 55 lbs. per square foot for #1s, depending on the species. (I used Douglas Fir-Larch.)

I’m assuming the joists will fasten to the ledger with joist hangers...not sit on the ledger.  So, I’d recommend a single 2x10 ledger (not a double), but it depends on the joist hangers you use. (The nails furnished with Simpson joist hangers are short and stubby. That’s because they take all the load in shear...and none in withdrawal.) You only need a single ledger, because you can fasten into a series of studs and a continuous double top plate...no spanning large openings. 

Therefore, each joist will need a joist hanger that supports about 400 lbs. for #2s and about 575 lbs. at each end. Likewise, you’ll need lag bolts that support about the same per foot. I’d use 1/2” x 4” lag bolt at about 12” oc. Best practices would call for the lags to be staggered along the ledger, but keep them a minimum of 2” from the edge of the ledger. 

Please note that this does not account for any seismic loading. If you live in a seismic zone, you may want to re-think this design, because the lags do not comply with withdrawal requirements for seismic requirements. 

Also, please note that the design loads are TOTAL LOADS. You’ll need to subtract the dead load (about 5 lbs. per square foot) from those design loads to give you an allowable live load. (Live loads are the things you’re storing.)