A warehouse under construction.
Construction is going on.
The warehouse mentioned in scentence one is under construction and scentence two is just a rewritten form of scentence one
exists x1 x2.(a_topic(x1) & under(x1,x2) & n_construction(x2) & n_warehouse(x1))
exists e1 s1 x1.(a_on(s1) & Manner(e1,s1) & Actor(e1,x1) & v_go(e1) & n_construction(x1))