Stairs with combined floor. How was this built?

[Darkstar_]

While exploring Altis, I came across a base in the early stages. But I found something which interested me. This is something I want to build but not sure how it was done. I can build a floor and stairs seperate but no option to combine them. How was this done?

 

[TheStainlessSteelRat]

look at staircase when placed and built and press ctrl+i to upgrade to staircase with floor, you will need extra lumber to do this.

[Darkstar_]

Is there a list of upgrades? So I know what can and can't be upgraded. Never knew about this, most posts I find talk about wall upgrades.

[Brez]

Maybe here: http://epochmod.gamepedia.com/A3Epoch:Arma_3_Epoch

 

I find youtube is the best to show you how to build as well as the trials and tribulations with it.