I would suggest you invest in the services of an experienced and qualified landscape designer. Unless one has a topographical map of the plot, generated at a similar scale, assessing and measuring slopes accurately is a complicated process and readily available design software will not address it.

Design only fees are relatively modest but well worth the investment if concerns about slopes, walls or terraces and other hardscaping - much more expensive and with potentially huge impact - are being considered.

At this point I just rough plan, not exact measurements down to the inches. YES, I do plan to hire a professional landscaping company with design services. they will likely have their own advanced software. HOWEVER, before I do that I want to bid out the work to at least three companies. Before I bid out the work, I want to understand what I am currently working with, and maybe even share on Houzz in order to get some advanced ideas. I don't need exact measurements but enough to give a rough idea. This will allow for a more organized bidding process. What I DON'T want to do is get an idea from one designer and then go back and get everything rebid from the other designers. Or worse yet, go down the road with a designer and a landscape design only to realize it was a big fail and then end up posting that big fail on Houzz in the middle of the project. I've seen it so many times on the interior remodel side on this site.

The thing to watch out for in landscape designing software is that most are not great on scale. While they won't let you make a tulip larger than an oak tree, most will not be that accurate. I doubt there are any programs at an affordable price worth using.

The point I was trying to make is that DIY design software is not going to help establish slope demarcations. You need a survey or laser transit or other level measuring device (less high tech ones are markedly less accurate) to accurately evaluate before you can impose them on any 2D design software, even professional grade software..

btw, I am not sure how familiar you are with landscape designers and the design process but one does not typically bid out design jobs. Installation contracts, yes - design only, virtually never. Spend the time you need now to research local designers skilled in the processes you need, review their portfolios and then determine how well you can work with them (establish rapport). Personally, I never react to a job bid request....it is just a business can of worms - without a scripted design plan, exactly what is one bidding on?? You are comparing apples and oranges. And rarely is this a profitable endeavor for any designer. You are essentially working without any recompense!

You could do a rough drawing by using Google Earth, assuming your lot doesn't have too much tree cover. That way, you'll have features to compare. Then, you measure slopes by rise over run, using string and poles.

Thanks. My lot doesn't have much tree cover. Will give that a shot.

Gardengal, thank you for your response. The landscape installers I've identified have in-house designers and design teams. I will not be using a separate designer and I'm avoiding installers that don't have the in-house design expertise. I prefer the two services to be integrated. I also don't want to go to them with a blank slate on what to design. I want to take to them a general idea of what I am hoping to achieve. When that is nailed down then they can do their accurate drawings.

Post photo of your yard here. You can get some ideas.

Here are some photos I already had on my phone.

First photo shows the gate to the side of our backyard. I include it because the fence line shows steepness of the slope along the eastern edge of our property. Area to the left (east) of property is green space. Second photo shows other side facing back toward the gate. Third faces SW and shows most of the backyard.

The flat portion is about 45' x 35. There is a french drain along the eastern (left) side of lawn that leads to a drainage pipe behind the yard. The yard flattens on the SE corner but then slopes downward. You can kind of see the drop-off in upper right corner of 3rd photo.

Doing any yard work on any of the slopes is a pita. This is why we want to hardscape perhaps with terraced retaining walls along the sloped edges to control for erosion and create better access. I want to leave trees and shrubs along the back fence in the 3rd photo. I also thought of planting a ground cover like bearberry for erosion. But doesn't help with access.
Located in PNW. Zone 8. Look fwd to thoughts/suggestions.

Some ideas are here

Thanks. I hadn't thought of the boulders. And it looks like something I can climb up behind to do some weeding.