Exterior Stairs

Looking to build a set of open stairs leading up to a deck constructed atop my garage. Deck is about 6 ft above grade; stairs sit on a C-slab poured adjacent to side of garage. As the deck is Duradek with a drip edge about the periphery of deck, the only means of fixing the stairs to the house is to put a series of lag bolts through the side of the stair top, through the vinyl siding and into the house.
The existing stairs are 2 x 10/2 x 6 construction (spruce/fir?) with treated 4 x 4 posts. Thinking of a series of 3 x 2x12 carriages and 1 1/16 x 11 1/2 OSB treads, all from spruce, maintaining the treated 4 x 4 posts. Looking for an opinion on these building materials as opposed to others. I'd look to a serious paint covering of the softwood as opposed to the treated stairs.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.