It all depends on your national insurance contributions. If you are paying class 2 national insurance contributions, then you are classed as having earnings equal to £130.20, which will then entitle you to Maternity Allowance of £117.80 per week, as long as you have been self-employed for 26 weeks in the 66 weeks prior to your EDD, and paying the class 2 contributions for at least 13 weeks in that period.
If you are self-employed but hold a small earnings exception certificate, then you will be treated as having earnings equal to the Maternity Allowance Threshold for earnings, which is £30 per week, which will entitle you to MA of £27 per week, as long as you have been self-employed for 26 weeks in the 66 weeks prior to your EDD, and held the small earnings certificate for at least 13 weeks in that period.
The other scenario is that if you have been employed in the 66 weeks prior to EDD, and self-employed, you can submit whichever details come out best for you, and you also submit your best earnings.
So, for instance, if you had been employed for 13 weeks, earning £300 per week, but now have a small earnings certificate which you have held for 13 weeks, you are able to cobble together the two types of employment, totalling 26 weeks, but submit the payslips from your employment, which would give you MA of £117.80 per week, as opposed to your small earnings exception, which would only entitle you to £27 per week.
Obviously, if you only close shop for 4 weeks, you can only claim MA for 5 weeks 3 days, as you would have 4 weeks closed, then 10 days as keeping in touch days.