Wall: (n) an architectural partition with a height and length greater than its thickness; used to divide or enclose an area or to support another structure
The particular definition of the word in English does not necessarily differentiate between walls, ceilings and floors in the way mentioned.
Function is what divides them. Technically a ceiling or a roof is a wall with a purpose to set an upper bound or provide shelter and a room is multiple walls defining a space.
With these semantics (words, words, words!), it is feasible to use the spell for floors, ramps, vertical or slanted walls, ceilings, floors, etc.
For reference:
[ Spoiler ]
Physical Barrier (Environmental, Area)
Type: P • Range: LOS (A) • Duration: S • DV: (F ÷ 2) + 3
Barrier spells create glowing, translucent force-fields with both 1 point
of Armor and Structure rating per hit (see Barriers, p. 194). The caster
can form the barrier as a dome with a radius and height equal to the
spell’s normal radius. The caster can also form a wall with a height and
length equal to the spell’s Force. The caster can adjust size of the barrier
the same as the radius of an area spell (p. 183).
Physical Barrier creates a physical wall. Anything the size of a molecule
(or less) can pass through the barrier, including air or other gases.
Anything bigger treats the barrier as a normal physical wall. Attacks
directed through a barrier have a –1 dice pool visibility penalty. The
barrier does not impede spells. The barrier can be brought down by
physical attacks, but as long as it is sustained it regenerates damage
quickly—any reductions in Structure Rating are restored at the beginning
of the next Combat Turn. If the barrier is penetrated, however,
it collapses and the spell ends. Physical Barrier cannot be used on the
astral plane.
Also, Ice sheet doesn't specify that it has to be applied to the floor specifically
so Ice man antics are hypothetically possible.
* ------[___ 
____]**********[____ 
