Surely you just need a router or repeater near the garden door unless you are bragging about the immense size of your garden.

I'm outside and have been all day. :-) 

I'm inside and have been all day

Thick granite walls don't play nicely with WiFi signals, I have to hard wire everything in this place. Plus the garden is rather yuuge.

I  am inside but keep nipping out to prune the roses in between ToDo items. It would be much nicer to be able to sit out there all day

I am sitting on a terrace in the sun drinking a cider. 

I had to move to my bedroom because it was too sunny and hot in the lounge.