High dBi Raspberry pi build

Hi folks,

I am looking to try and build a piratebox that has a good dBi signal strength to try and make it accessible for as large an area in my block of flats as possible. With my wireless router I am able to still receive a signal in the stairwell from the ground floor up to fourth floor (I am on the second) and that's with it positioned on the far side of my flat. I am planning to place a pi running piratebox in the room next to my front door to see if can get it to broadcast further. I was wondering if folk could provide any advice on what the best options might be for maximising my signal strength?

Also wanting the pi to be able to access the internet for my own uses. I assume I can use any compatible dongle and connect to my wireless normally.

My current thinking therefore, in terms of providing piratebox access - I have an old wireless extender router that I no longer need, might it be possible to install custom firmware on it, set it up with no password to access wireless, connect it to my pi via cable, and then set port forwarding for http and https to the pi and let the piratebox software do the rest of the work? Or would I need to add some further steps?

Cheers,

Brydie.