You are getting fixed price quotes labor + materials, but you wont actually be able to get accurate figures by knowing labor costs because what they are charged by the suppliers and what they mark up passing on to you will make a difference compared to if you purchased the materials and did the labor yourself. You could ask them for a breakdown.

So you want to shave of $5000. off of a quote of $5670.? Do I read this right, or is this a figure you just used as an example?
I think you don't understand the components of a quote. From the post, your version is labor and materials. This is not the case. An estimate(from a contractor, not a handyman) has four components. Labor, material, profit and overhead. Say ,for arguements sake, that your $5200. roof was on a ranch and consisted of 14 squares(1400 sq ft) of roofing. The material cost would be around $1000. for a 30 year architechural roof. The rest would go into the other 3 categories. The amounts would vary from locale to locale and contractor to contractor, in each group.
Do you ,"save" $3800.? No, you need to pay to have the old roof carted away, unless you're one of those people who slaps another layer on and saves the labor and money. In my opinion, a bad idea. It doesn't allow you to check out the condition of the roof deck and add improved roofing technology that's come along in the last 40 years.
While there are always ways to save money on a large job, it should be done intelligently and not be just a checkbook thing.
When I quote a job, I don't break it down catagorically. It's none of the customers' business what my overhead and profit are. They look at the bottom line and decide if they want me to do the job. When you buy a $20,000. car, do you get a breakdown? No you don't. They would look at you like your nuts if you asked.
Ron

Sorry, I should have been more specific. We have a quote to do numerous improvements (frame in mudroom, raise roof line for that mudroom, expand kitchen, new roof, new siding, etc.). From that quote we need to shave off $5K and we were wondering about how much we would be able to save by doing the roof and siding labor ourselves.

I have several years experience in building HfH houses and can do several different kinds of siding. I can do roofing as well-----but would never attempt my own roofing---too time consuming and dangerous in many cases.

The siding can often be DIYed easily on a single story house. Siding on a two or more story house is less DIY friendly, due to the need for scaffolding.

Another place to save is the work after the framing---sheetrocking, painting/wall treatments, trim carpentry, and flooring. All those areas can be a DIY money saver.

Roofing is probably not something you want to do yourself, especially if you have more than one layer of roofing. But it is doable if you don't mind lots of labor and some risk.

To determine how much you might save, take the number of squares from their estimate and find out how much HD would charge. Then get a price quote for a dumpster & haul away.

If you decide to do it, be sure to get the delivery option that uses a conveyer to put the shingles on the roof for you.

Roofing is doable depending on the type of roofing and the type fo building. In a smallish one-story ranch that does not have a steep slope to the roof line, using asphalt shingles, it's hard labor, but definitely doable (I recall being up on the roof handing Dad nails as a kid). Bigger houses, steeper roof lines, multiple changes in the roof line, multiple stories, cement, tile, or other heavy roofing product -- not as DIY friendly.

Other areas to save are in doing the demo work yourself. Depending on the type of flooring, flooring can be pretty DIY friendly. Painting is definitely DIY. A lot of plumbing can also be pretty DIY friendly. Finish work in general is usually a safe way to shave some costs.

I would be upfront with the contractor and ask for his advice on what you could do yourself to save money. A good contractor will be reasonable and honest, knowing you are being upfront. I would not attempt any project, however, without understanding the details, time, skills and tools involved. I've done many types of projects, but roofing is not on my list of things to try. Too much at stake. And, FYI- labor often is 25 to 30 percent of the job, but will vary, obviously.

another option is to be you own GC. We ended up firing our GC 2/3 of the way through the project. We GC'd the siding, painting, flooring, kitchen, master bath, heating, interior trim, deck and landscaping. You end up having a lot of control on the budget. Beware, it lengthens the time frame...a lot!!!

Roofing and siding are not that easily done....if you have no experience consider timing out your project and budget. We are "fixing" a 60K bad roofing job right now. It isn't easy and it is very expensive for the homeowner to get it fixed. Same with siding.

Roofing and siding are what keep water out of your house and water does more damage than you can imagine. They are two things I'd never consider DIY'ing and I just don't think you'd save enough to make it worth while in the long run. Leave those to the professionals and find other ways to save money either in the quality of finishes, DIY the demo and framing, maybe tile, maybe flooring. There are lots of places on line to find materials at low cost too.