Building a matrix with a varying column length

I am trying to build a matrix whose rows are as many as the length of D (see below) and whose columns vary. Because this is impossible I tried to preallocate the size of the matrix trying to fill it with zeros. Unfortunately I get the following error:

Subscripted assignment dimension mismatch.

Below you can see my code

n=1:1:2;
  D(:,1)=L./(2.*n);
    % Wf=20*10^-6:10^-6:L;
    % S=zeros(size(Wf));
    Wfmin=20e-6; 
    Wf_step=1e-6; 
    Wfmax=2*max(D); 
    size=length(Wfmin:Wf_step:Wfmax);
    for i=1:length(D)
        Wf=zeros(i,size);
        Wf(i,:)=20e-6:1e-6:2*D(i);
    end

Answer 1

[Walter Roberson]

T = 20e-6:1e-6:2*D(i);
Wf(i, 1:length(T)) = T;

Answer 2

[Giorgos Papakonstantinou]

Thank you Walter