Location, location, location
This is fairly easy you need a giant stone building in a dry tectonically inactive area, which carved and possibly inlaid writing in stone on the inside.
Out of all humans structures these last the second longest, the longest lasting are carved directly into the stone, but those are also hard to find especially from orbit or aircraft. Clay is good, stone is better, inlaid stone is best, granite inlaid with gold is about as indestructible as you can get on earth. It is also fairly easy to make; carve stone, pour on liquid gold, rinse, repeat. writing no matter what it is needs to be protected, even paint lasts tens of thousands of years in cave, inlaid stone can easily last what you need, you just need to build an artificial cave. Note another good question would be what kind of "rosetta stone" to leave behind so they will understand what you wrote.
A massive block of stacked stone is the best protection against erosion. A dry climate will also keep erosion to a minimum. the pyramids are not bad but their location is not great, it is a little to erosion/burial prone, a colder climate may be better. If the outer cover of the pyramids had not been stripped off by people they would be far more resistant, and would not be as bad a shape as they are in But the location is the most important part, some place with minimal erosion and burial, non-sandy deserts for preference, egypt has too much shifting sand and deposition. the Nasca desert would be a great pick, although if you can find a less geologically active place even better. Honestly a question just about location might not be bad.
Dating it is really easy he just needs to leave several blocks (like inch cubes) of different radioactive material with the original ratios of parent and daughter material written on them or their stone container. carbon 14, potassium, and uranium will be good choices, plutonium is even better. If you can have a few blocks of uranium glass in a different area of the structure that will allow fission track dating as well. the nice thing about dating methods are the more you have the smaller your error bars get.
The hardest part is getting spotted, first it need to be an unnatural shape, like a triangle or square (another reason pyramids are good). if you can have consecutive shapes even better. three structures laid out in a triangle are even better they get noticed. Alternatively dig a giant triangular hole and fill it with concrete, that will stick out like a sore thumb on regular and gravity maps. Put your structure right on top. keep in mind structures don't have to be that big to be seen from space, many large buildings are visible with only minor magnification. If you can put it in geologically weird location even better, like right in the middle of the painted desert, or ayers rock, or large flat expanse so it stands out.