Gap at bottom of steel security door

Hi, I'm going to install some bifold (folding) doors, but need to prepare the door frame. I wondered if anyone knows how the inner blocks of the frame should be built? Presumably, if the door folds outwards the two blocks on either side of the frame are not opposite each other, as with a normal door frame, but one is on the outer edge of the frame, the opposite one on the inner. Is this correct? Thanks for your help. Kevin

Hi, Guys: This might be the repeated question but I do want some specific answer for it. I try to replace windows in my bedrooms besides road because we can hear some noise (a little lound in the daytime). We try to use Double hung window with options like LoE, gas etc. We went to Homedepot and Lowe and got a lot of information. But the problem now is that we know too much to decide to which one to choose. There are brands we got so far: Certainteed, and Simington,pella, American craftsman. Which one should we choose and should we buy directly from homedepot or low? Is there any other special option we can pursue for noise attenuation? Also, one sales people suggest we use construction window instead of replacement window? The difference, he says, construction window provides more seal than replacement window. Thanks, guys!! Acton