Instead of permanently-installed steps with the flashing issues that may ensue, may I suggest you get a roof ladder with roof peak hooks and just hook it over the peak and leave it installed. It's not really noticeable most situations and provides ready access for a host of roof-top jobs..

You can even get ladder hooks with rolling wheels that make it a snap to roll it up and hook it over the peak.

I do the slate repairs on our seven two-story plus buildings, and of course you can't walk on slate. We also heat with wood so have frequent needs to go up and clean out chimneys.

We keep a ladder permanently just lying on the backside of the roof right next to the chimney. Then all we need to do is raise an extension ladder to the eave and step right on to the roof ladder. On a different wing we keep another roof ladder permanently on the roof to access our private cell service repeater (it needs tweaking after every big windstorm, alas.)

The roof ladders are just single leafs of an appropriately-sized extension ladder taken apart (a two-fly ladder yields two sections that are used independently.) I think the reason we do that is it is cheaper than buying a single ladder that long. We got the last one at Home Depot or Lowes.

I buy the roof hooks from the source below because I often take the permanent ladders off to work on other roofs. Having wheels enables me, a smallish-sized woman, to easily slide 16 and 20 foot ladder sections right up to the peaks and hook 'em over.You can find non-rolling ones in many places, and that may be fine if you aren't moving the ladder very often.

I think that having a ladder would be safer than stairs, because the ladder will help you keep in mind that you need to keep your weight into the roof. You can get in real trouble standing upright on a roof as if it was level ground.

If your roof is really steep, you should be wearing a fall-protection harness system. I do on our tallest and steepest barns, and my DH who works for a solar company uses one every time he's on a roof. You can get harness systems from this same source, which specializes in roofworking (especially for slate and metal roofs) supplies and tools. I have been their customer for years, and never been disappointed. They have all the good - and often hard to find - stuff needed for slate work (except the slate!).

HTH

L.

Here is a link that might be useful: Roof hooks with rolling wheels

The only safe way to have permanent year round access to your roof is to have a metal shop fabricate a permanent steel staircase, attached at the ridge and the eaves. It would be made so the treads are expanded metal mesh, at an angle so they are all horizontal to earth, and with handrails.
Your brackets will wear the shingles, probably come loose at the fasteners, and the wood will become slick with mold in wet weather, icy in cold weather, and break down over time.
Roof jacks as pictured are temporary.
Casey

Thanks to all replying. I am not a fan of the ladders because those cost about just as much while not giving the same comfort and convenience.

I got the point of wearing the shingles by the wood planks, but my plan was to use 2x4s instead of 2x6s -- and have a gap between the planks and the shingles. This would keep the wood from touching the shingle (except where the bracket is already touching it).

The nails holding the brackets will be covered by the next layer of shingles (and thus not exposed).

I understand, that a custom-made all steel staircase (with railings) would've been better, but that's way too much money and trouble. If I planned on walking out there regularly -- may be. For a twice a year exercise it seems like an overkill...

Thanks again!

The heel of the metal bracket sits on the shingles, and nails are very temporary, you would _have to_ use screws.
Of course, you only need a pair about every 32", you pull yourself up from one set to the next.
You will inadvertently rub the gravel off the shingles at the level of the 2x from foot contact.
Casey