So charged particle radiation doesn't travel in straight lines. Obviously, it is an energetic particle so it's moving in some direction, but as it does, it interacts with atomic electrons and forward scatters adding some randomness to the path. It is these atomic electron interactions that are the "ionizing" part of "ionizing radiation".
The interaction is described well by the Bethe-Bloch equation.
$\alpha$ and $\beta$ radiation are the primary charged particle forms of radiation. The alpha is a helium nucleus and it is stopped by a piece of paper. (It's slow moving and has a charge of +2). The biggest danger for alphas is ingesting a source...then it can sit in your body and depositing damaging radiation in vivo for a long time.
Beta rays are beta-decay electrons (or positrons), and they are bit more penetrating...but they should not make it through the roof and the floor, and the air in-between. Electrons are light, so beta rays are generally relativistic, hence they deposit energy at slower rate, and travel farther.
$\alpha$ and $\beta$ radiation are also the most significant for fall-out, as neutron rich fission products work their way back to stability.
Sometimes the decay will leave the daughter nucleus in an isomer, which is just an excited state of the final state nucleus. The isomer will then make an electromagnetic transition towards the ground state, emitting a $\gamma$ ray, which does indeed travel in a straight line. (Cobalt-60 is a classic example).
$\gamma$ rays are neutral, so they penetrate. They do not leave an ionization track (a characteristic of charged particles). When they do interact, via the photoelectric effect, Compton scattering, or pair-production, they produce other charged particles that do damage.
So the best thing to do is: leave them on the roof.
You can look up the "radiation length" of various materials here:
and see what the fall-out emits here:
and get more details about the passage through matter here: