I often have to ask clients to obtain topographical surveys before I can start design. It is necessary for complex terrains.
That being said I have had some moderate success using my Garmin E-Trex taking spot elevations on sloping lots. The conversion of the data into AutoCad & then into Archicad is difficult at best since the scales are way off. Once you find a scale that matches the lot information, you have a cm accurate survey - providing you spend lots of time at each spot to get accurate readings. It won't match real-time elevations and may be off by meters but it will be all relative. If the first point is off then all the rest will be too. Its relative.
Other times, I have enough experience in my 40 years in construction/inspection/design to estimate the general slope of a lot by walking it. This is the simplist method.
Finally, you might want to get familiar with basic surveying techniques. On occasion I have gone out and taken my own shots relative to a known benchmark near the site. It doesn't have any use contractually since I'm not a surveyor, but it offers a way of capturing key features of the topography for design purposes. However, before the contract drawings are finalized, I would still insist that the client undertake a proper metes and bounds and topographical survey to make sure the elevations around and placement of the the building are properly represented.
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