Background: North Texas area (Collin County). Slab on grade. No basement. Soil is clay. Existing grass is Bermuda. We have a small backyard. It is roughly 30'x40'. The corner of the property was sloped off towards the alley as you would expect to promote drainage. It had excellend drainage but the slope was too great to be usable. There was an existing 2' retaining wall on one side of this yard area that also sloped down to the corner. And there was a soon to be large Cedar Elm tree right in the corner. The upshot is we wanted to reclaim the space, however small, for use as a play area for the kids. I have done a few things:
1) Removed the tree.
2) Extended the 2' retaining wall around the back of the yard so that it is level with the existing retaining wall, back-filled the wall with about 12 inches of 3/4 angular limestone gravel in a landscape fabric envelope, and put a fence on top. BTW, the height of the retaining wall at the highest point was 20 inches so I didn't do a draintile - just gravel.
3) Installed 4 inch sewer pipe (white) for all of the gutter outlets to this area and daylighted them through the wall in the corner.
4) I put in a 12x12 basin + drain grate in this back corner. In fact, my gutter drainage pipe is all tied in to the basin. Not sure that it will actually be useful as a drain though.
5) I redid the entire sprinkler system from scratch in the area so the heads can be properly adjusted to the new level.

Now I am at the stage where I am bringing the back yard up to level with the retaining wall and re-setting the grading. The area will be topped with turfgrass (Bermuda). Since it is a blank slate, I want to get the soil and grading right for drainage and grass. I have been filling the area with Texas Black which is very fine, clean, clay fill dirt. This is going on top of the existing soil which is almost all clay and rock. I know that I can't put grass down on the clay fill dirt so I must leave room for topsoil.

Grading questions:
- Note that the area in the picture only takes water from the surface itself. The rain from the gutters in this area have been daylighted though the wall.
- Should I grade so that the drop from house to edge is gradually but monotonically increasing? Like a mound or an upeside down half parabola on its side? Or should I go for more of a straight grading from house to to edge? I've seen it done both ways. By the way, the elevation change I have to work with is 12 inches of drop in 300 inches of run for the 2 most distant points from house the edge of lot.
- Since I have a clay base and I will be putting topsoil on top, should I grade the clay a certain way and do the final grading with the topsoil differently? In other words, would I want to create some hidden swales in the clay to direct water to my drain but fill in the swales with topsoil/grass on top to have a better final appearance? Am I over-thinking it?
- My drain 12x12 drain. I'm not sure the drain will actually be useful in my small area but at this stage, I can do anything I want in terms of the elevation of the top of the drain or even taking it out. Right now it sits about 2 inches below the edge of the lot (wall). I was thinking grade the clay to direct the water to it but the final grading of the topsoil would not obviously deliver water to it.

See two pictures attached for more details. An better view can be obtained here:

http://imgur.com/a/yQgGv

Thanks in advance.

eltbee

Also I did some testing with saturating the area with sprinkler water and it does seems like the grading is delivering water to the back corner. Kind of playing it by ear on the grading one truck load of dirt at a time. Still love to have input on final grading shape. Also, I bought a 36 inch landscape rack. Best tool ever.