What is the best solution for Wi-Fi Extender from the main home to a wooden shed?

1. AC1900 is a speed. not a model. 

2. the shed is a challenge. 20 meters isn't that far of a distance. the problem is that the exterior of homes tends to block signals very well. this happens because they're made from materials that have components to them that block signal. things that block: foil lined insulation, metal siding, concrete, brick, concrete board, etc. Same with sheds. they tend to be made from metal and metal blocks wifi signals. 

the best thing for you to try is to get a short extension cord and connect the extender to it and prop the extender up in a window. (glass doesn't block wifi). Then go outside to the shed (both right outside it and inside it) and test if you can get a connection to the extender and test the actual speed you get (speedtest app). 

that'll tell you both if a extender/satellite could get a signal to the shed and if that signal will pass through into the shed. Its your best hope for testing before buying anything. If it can reach but not get into the shed because of the material its made from, then you might have to look at a different option like burying an underground ethernet wire.