House is 1997 construction - slab foundation - original carpet. In process of updating and want to install laminate all rooms. Home Depot did the measurements and once order info I noted there could be problems with doors and problems with the slab - level issues. I have noticed a hairline crack in one bedroom under a window. Several years ago the baseboards in two bedrooms had a separation like issue occurring on the end corner. I have no idea how much any leveling work could cost in addition to product/installation but was told if I went with carpet in the 2 back bedrooms any leveling wouldn't be required. My house is the first house the builder built and I am somewhat worried about what issues the slab may have. Any recommendations or input regarding this matter - I'm new to the game. I'm afraid this project may end up going way over budget and have to spend money I have marked for other improvements.
It depends how out of flat your slab is and how perfect you want the installation.
The slab doesn't have to be level but it should be flat. You'd need to remove the carpet and use a straight edge and look for gaps while moving the straight edge around the room. Generally it doesn't matter how new the house is - slabs are never perfect.
Door bottoms can be cut down if they are paint grade fairly easily also if there is already carpet then you likely will already have enough clearance.
It also depends on the installation type. You could be doing glue down, double glue down, or floating, unlikely to be doing nail down. I'll assuming floating as this is the easiest. I'll also assume that the underlay is built into the laminate flooring.
If you don't care about noise - the squeaking of the tongue and grove as you walk across the floor - then you can probably install with a fair amount of variance in the slab. If you want there to be zero noise then you'll likely have to do at least some spot leveling. There are some techniques you can apply to avoid noise in bad areas like gluing a few planks together to span an area with flatness issues. Some people will spot glue a few planks in key locations though you have to be careful to consider expansion and how that will work if you fix those boards. If you apply these technique you won't have noise but may have some bounce to your floors - some of this comes down to how good the laminate is (thickness, quality of the mechanical attachment, etc). Generally the most important part of the installation of the floor is the prep work and this includes getting the substrate as flat as possible. Grinding out high spots and spot filling low spots.
The flooring manufacturer typically rates the expectation for flatness over a ten foot distance. Engineered hardwood for instance typically requires 3/16" difference over 10' or 1/8" in 6'. This is for optimal installation and I'd bet that very few professional flooring companies actually get the floor to this degree of flatness. Glue down floors can generally accept larger tolerances as the floor is glued to the substrate and won't bounce. I have a glue down engineered floor that was installed by a high end hardwood flooring company, they used the self level flooding method, but this floor is still out by 1/4" in 3' and the flooring looks fine and there isn't any obviously detectable flatness issues even though the manufacturer specs 1/8" in 6' which is 4x more flat than what the flooring company achieved. The rooms I have this floor in are bedrooms though and a large portion of the rooms are covered with furniture. Again this kind of thing can factor into the decision on how extreme to go. If you are going to cover the floor with a large amount of furniture and use area rugs then you can opt for more flatness defects. If you are going for a large open space that won't have furniture then you'll want to pay more attention to the flatness.
Flatness between different rooms can be worked out with custom transitions in door ways.
Floor prep is fairly complex and probably not done to high degree of perfection even with most professional installers.
My recommendation would be to get a 6' flat edge, remove the carpet, move it around the space for the floor, note any dips that are more 1/4", note any high spots. Address the worst ones - I've seen people use mortar to fill in low spots. You are probably unlikely to have super high spots so you can probably avoid any grinding. Aim for flat with no dips more than 1/4" over 6'.