1. If you are hiring someone to gut and then rebuild a room, if the floor above has slopes this is the time to fix it. If the person who did the gutting of room (apt in this case) does not know structural things then bring someone in who does. Do not skimp on the boards or beams. A couple of 2*6's over a 12 foot span does NOT support a room above it that is 12 * 12 that has a bathroom. It simply cannot carry that amount of weight. There are tables to figure this out.
If the middle of the building has a sag going down this means the issue is in the floor beneath or in the cellar. If its a cellar placing an adjustable metal crank up jack on a 1 inch concrete cellar floor is not the answer. The cellar floor will give over time & you will have the sag. A far better solution is to dig a 4 foot hole and pour concrete and place the new support on the dried concrete. Most of construction work is quite dangerous so its better to have someone doing this that knows what they are doing! One does not want to have the building collapse.
If the walls and ceilings are open install the new wiring now as its going to be a whole lot more expensive for an electrician to snake wires when the walls are closed. Place 3 way switches at each end of the large rooms like kitchens. Install your cable t.v. wire and cat 5 telephone wires. If its a kitchen place enough circuits on the countertop. And use double and triple ganged boxes so you can have more outlets in the finished product. One outlet on a long countertop is certainly not enough.
Change the windows while the walls are open. Or at least measure and order them and frame for the new ones before closing the walls.
Do not allow the insulation to be in stalled or walls to be closed with sheet rock until someone who knows structural, electrical & plumbing has looked. It could save you tons of money - or your family's life.
2. If you are doing an outside deck and set of stairs. Here in the northeast the supports should be down 4 feet and be filled sonno tubes. Its best to have them come a foot above ground. We like to install the bolts in the drying concrete and then a metal bracket that is about an inch high. This allows air to flow underneath the wood that will sit on top of concrete. This way the wood will last longer as its less likely to rot out.
If you are going to have steps running from the new deck down the rule here is 7 inches max height between risers. If its 8 inches there is no inspector that I know of that is going to sign off on that. So before the "reasonably priced contractor" is fully paid make sure that the steps and rails are code compliant. It could be on your dime to tear it all out and do it right at some later date.
Most deck collapses occur away from the house. Many are caused be not having them secured properly to the house.
If you are going to use a different kind of man made wood beware that some of the hardware fasteners are rotting out 4 times faster than normal with p.t. or pine lumber. You might want to make it so there is some sort of access to change that hardware when someone figures out the correct metal for the type of wood you are using.
My rule is no work for family or friends. I do not have the health anyway. I really do not like to criticise other people's work BUT when things are as bad as above its a safety issue for many years to come. In number 1 above I would have leveled the entire building and gone prefab but the homeowner said that they are "too far along". Oh they might be in 20k BUT I could see a whole lot more being spent and the end product sloped, slanted, and unsafe. Some people ask for advise but they just won't listen.
Now being curious - how do the rest of you contractors handle it when a good friend's wife asks you if it a "good job" that they had done??? I am not talking about if a molding is not square or a tiny slope in a floor.