Where do you live
You are a little far up to have year round flourishing grass like normally seen on most golf courses which is bermuda or zoysia.
You need to level out a spot about the size of 10ft X10ft. Go to your local lowwes and buy about 15 bags of topsoil and about 5 bags of sand. If you would like an elevated box I recommend you surround the area with cross ties. You will need to place your topsoil out and add in the sand. Then use a tiller to mix it together then spread whatever grass seed you choose. Then rake the soil out to a flat surfaceand throw out a little more seed. Then cover the ground with straw or hay. The water the area every night for 2 weeks then every other day for tyhe remainder of the month then when the soil is dry for a total of about 2 months. Let the grass get up about a foot before cutting it back on the highest mower setting. Over the next few weeks keep mowing it lower and lower. The lower you get it the more it needs to be watered.