I assume by having same variables in all the excel files, the different dimensions that is mentioned in the question represent different number of rows present in those excel files. I suggest appending all the excel files into a single table by reading each excel file one by one and adding it to the table. For reading one excel file into a table you may usereadtable. For joining two table you may use following
table_1 = readtable(filename_excel_1);
table_2 = readtable(filename_excel_2);
new_table = [table_1; table_2];
For creating a lookup table, I assume you want value of a single variable which have dependency on all other remaining variable. For this part you may findthis Answeruseful and you can use interpnfor creating the lookup table.