Bicycle basket dimensions?

Go to Walmart or wherever you bought the bike. Find a similar bike and find out if your measurements for the basket will work.

What are the chances someone who answers questions here would have that same bike? 0.00%

First think through how you will be attaching the basket to the bicycle, as that may affect the way you construct it.

Then I think you really need to measure the bike, although that may slow things down. Think of things like making sure the basket will not foul the lights or the brake or gear cables.

You haven't given this very much thought. When you start a project the first thing you have to do is to take measurements. You are expecting that there may be someone who is willing to do that work for you. Are you willing to pay someone to do your work? Next, do you know anything about bike baskets? Have you ever made one before? Do you have any idea about how you will attach it to the bike? How many baskets are you prepared to make before you arrive at a suitable design? The only way you will succeed is by having the bike on hand so that you can take your own measurements yourself.