There are a number of different chicken coop designs out there. You don't need a walk-in coop, but like you realize, you should be able to access all parts of the chicken coop for cleaning, maintenance, etc... Some designs are better than others. If I were building a small elevated chicken coop, I would look for a design with a drop down back wall or something like that where I could easily reach inside and put my hands on anything I needed.
FYI, in Square Foot Gardening, they recommend only building something about 2 feet wide for easy reach, and maybe a 3 foot reach at the most. You could probably get by with any of the small coop designs built no bigger than a 4 foot reach if you used a small rake or handy reacher to extend your arms.
I built my coop on an old boat trailer frame. It is 6X12 feet. Although it is walk-in coop, I can access the nest boxes from outside and I have the feed and water at the back panel doors. I rarely ever have to go inside my coop, given the thought and planning that I used before I built the coop.
I would also recommend trying to find a design that uses deep bedding in the coop, with a drop down panel(s), so you can easily clean out the coop when needed. Many of us with deep bedding systems only have to change out the coop litter maybe once or twice a year. If you go with a pull-out drawer, you will have to be cleaning it out all the time, and those drawers are notorious for breaking down and falling apart after a short period of time. I would recommend you avoid that drawer trap.
Like so many others have already commented, there are many, many, advantages to having a walk-in coop. If that is not possible, look for a good design that allows you easy access to all the corners of the coop so you don't have to crawl and/or bend over to clean it out. Best wishes.