In your case:
a = 3:5;
v = [0,-1,1];
n = cumsum(a,'reverse');
C1 = nchoosek(1:n(1),a(1)); % Here are the two calls on 'nchoosek'
C2 = nchoosek(1:n(2),a(2));
M = ones(size(C1,1)*size(C2,1),n(1)); % First, fill M with all 1's
k1 = 0;
for k2 = 1:size(C1,1)
p1 = C1(k2,:); % Use C1 to generate indices for inserting 0's
q1 = 1:n(1);
q1(p1) = []; % These indices will point to -1 and 1 locations
for k3 = 1:size(C2,1)
p2 = C2(k3,:); % Use C2 to generate indices for inserting -1's
k1 = k1 + 1; % Advance the row index of M
M(k1,p1) = v(1); % Insert 0's
M(k1,q1(p2)) = v(2); % and -1's
end
end
