Depending on what you're doing with the lawn as a landscaper, I will say it is much easier if "we" come in at the very end (last) if at all possible just so that we are not in the way of other contractors and they and their vehicles are not in our way things go much smoother. As for the roofer and landscapers at the same time, unless you have landscaping tasks that need to be completed away from the house as well it is an issue we are always in each others way, as roofers generally take and just throw their stuff (trash & debris) on the ground ALL around the house.
Also any contractors performing "major" jobs that require bulk materials to be on the job site will be in the landscapers way, again depending on what other tasks you have for the landscapers. Many contractors also like to or need to in some cases drive onto the lawn for ease of install of appliances, use of equipment such as lifts and fork trucks. In all honesty if at all possible try and always schedule your landscaper for last. You don't want them to come do your lawn and have it looking beautiful to have a contractor come right behind them and drive on it ruining it. You also don't want the landscaper to have to leave your project because another contractor is in the way or blocking access to an area they need to get too for the their next task, so they go to another job and than your project gets "set aside".
Best advice is communication is key, if you don't have a GC or Project Manager running the show tell each contractor what other tasks you need done and ask them if those other contractors will be impeding their ability to perform the tasks you want them to complete.
Being a crew leader if a crew calls me and says they are stuck and can't go any further due to another contractor being in the way I am sending them to the next job location, I will not pay them to sit around until the roofer is done. That down time is not figured into the quote.
There is a reason why many times you drive by new built houses that are finished besides maybe some interior finish work and the yard/lawn has still not been touched.
That is also the benefit to hiring a GC and why you pay them what they do because they are responsible to deal with all those headaches and problems, we pay people to make problems go away.