Underground shelters can be a DIY project as long as the water table is not at or above the lowest point of the shelter AND the ground is stable when dug. Even unstable ground can be dealt with as long as there is no water, but it is more trouble and time consuming. It will pretty much have to be a dig and cover. Digging out underground can be done, but I do not recommend it to anyone that basically has not already had some direct experience do it. It is too dangerous and I simply do not feel comfortable suggesting anyone do it.
For break-ins, either planning and practicing immediate reaction drills and keeping appropriate weapons at hand at all times, or doing an escapable safe room are pretty much it.
Getting into an attic during a break in is problematical. If you have time for that, there is a chance you would have time to get to your survival shelter, depending on its location. Again, depending on the design of your home, it would probably be better to armor the room closest to the primary point where the perps would enter the home. This is not necessarily the front door, though it might be.
But, as will probably be pointed out repeated by others, having a safe room can be 'a death trap'. Which can be true, if (just like 'bunkers' and other 'fortifications') it is not designed properly. With ventilation that cannot be compromised, and a way to get out safely if the perps either are close to penetrating the space, or they are setting in for a siege that you cannot out wait. And there are ways to do both, despite absolute refusal by some to believe it.
For your situation, again depending on the particulars of the house and ground, a shelter that can be quickly and easily accessed from inside the house, with that access easily blocked once you enter, and a couple of alternate ways to get out without being discovered, would probably be easier, cheaper, and safer than two different shelters.
But being ready to react, and having the means to do so if there is a home invasion or even just a simple break in while you are home, is the cheapest way to deal with such events. But it takes a commitment to train, and stay proficient.
You will need as much warning as possible in any event, so install some early warning methods, as well as deterrents.
Just my opinion.