High Gravity Mead
As mentioned in the sidebar on kveik in the Yeast section, kveik yeasts almost completely change the rules for high gravity meads. The comments in this section still apply if you're using traditional yeasts, but if you decide to experiment with kveik yeasts, you'll find your meads are done more quickly at higher alcohol levels than were previously possible.
Just like other meads, except more so. When I speak of high-gravity meads, I mean mead in the 4-lbs-honey-per-gallon-of-water range. The added sugar means it'll take longer to ferment. It also makes it very likely that you'll need a yeast nutrient.
Another issue to consider is that most yeasts don't do well under high-sugar conditions. The things to remember are the same as for other meads, but you'll need to expect longer fermentations (having to wait three or more months for fermentation to slow is typical), and once the fermentation is done, these meads typically take longer to age. Given enough patience, you can make some very tasty, very strong meads of a traditional style.
Meads of this style were traditionally started in the summer for consumption in the winter or spring. This will work out nicely from a temperature standpoint, as you'll have warm temps to start the yeast off quickly, and then cooler temps to age the mead once it's mostly fermented. However, these meads are not for everyone. With this type of mead, you'll probably want to rack the mead (transfer it from a primary to a secondary fermenter) twice, as having the mead sitting for prolonged periods on the dead yeast will add off flavors to it. The results are typically worth the wait, though.
A way to speed the process is to add the honey in smaller batches. For example, if your recipe calls for 20 lbs of honey in a five-gallon batch, start out with 10 lbs initially. Once the fermentation starts to slow down, rack the mead into another fermenter and add 5 more lbs of honey. Wait for the fermentation to slow, rack again, and add the last 5 lbs. If you take this approach, make sure to leave some room in the fermenter for the added volume of honey. Adding the honey a little at a time like this will keep from hitting the yeast with high-sugar conditions which aren't good for them. The yeast will repay you by doing their job more quickly, and you won't have to wait as long for a finished product.
This is a good area to get into once you've made a few lighter gravity meads and have gotten some extra equipment, since you'll be tying up a carboy for at least six months.